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Methods (Functions)
CSE 1310 – Introduction to Computers and ProgrammingVassilis Athitsos
University of Texas at Arlington
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Terminology: Methods/Functions• In Java, the term methods is the one mainly used.• In some other languages, the term functions is more
common.• In some languages (e.g., C++) methods and functions
have minor differences in meaning.• In this course, I will use the two terms (methods and
functions) as synonyms.
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A First Example
• Here we see our first example of a function.
• It is called square.– Its job is to
compute the square of a number.
import java.util.Scanner;
public class example1{ public static double square(double number) { double result = number * number; return result; } public static void main(String[] args) { Scanner in = new Scanner(System.in); System.out.printf("Please enter a number: "); double N = in.nextDouble(); double N_square = square(N); System.out.printf("%.2f squared = %.2f\n", N,
N_square); }}
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What Is a Function• A function is a piece of
code that does a specific job.
• Usually (but not always) the job is to compute something.
• Examples:– Computing the square
of a number.– Determining if an
number is prime.– Computing the number
of digits of a number.– Counting the number of
vowels in a string.
import java.util.Scanner;
public class example1{ public static double square(double number) { double result = number * number; return result; } public static void main(String[] args) { Scanner in = new Scanner(System.in); System.out.printf("Please enter a number: "); double N = in.nextDouble(); double N_square = square(N); System.out.printf("%.2f squared = %.2f\n", N,
N_square); }}
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How to Write a Function• Specify a name, like
square.import java.util.Scanner;
public class example1{ public static double square(double number) { double result = number * number; return result; } public static void main(String[] args) { Scanner in = new Scanner(System.in); System.out.printf("Please enter a number: "); double N = in.nextDouble(); double N_square = square(N); System.out.printf("%.2f squared = %.2f\n", N,
N_square); }}
function name
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How to Write a Function• Specify a name, like
square.• Specify the inputs
(called arguments).– The arguments are the
input that the function needs in order to compute an output.
– For example, what does the square function take as input?
import java.util.Scanner;
public class example1{ public static double square(double number) { double result = number * number; return result; } public static void main(String[] args) { Scanner in = new Scanner(System.in); System.out.printf("Please enter a number: "); double N = in.nextDouble(); double N_square = square(N); System.out.printf("%.2f squared = %.2f\n", N,
N_square); }}
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How to Write a Function• Specify a name, like
square.• Specify the inputs
(called arguments).– The arguments are the
input that the function needs in order to compute an output.
– For example, what does the square function take as input?
• A number.– We can have functions
with 0, 1, or more arguments. We will see examples later.
import java.util.Scanner;
public class example1{ public static double square(double number) { double result = number * number; return result; } public static void main(String[] args) { Scanner in = new Scanner(System.in); System.out.printf("Please enter a number: "); double N = in.nextDouble(); double N_square = square(N); System.out.printf("%.2f squared = %.2f\n", N,
N_square); }}
argument(s)
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How to Write a Function• Specify a name, like
square.• Specify the inputs
(called arguments).• Specify the return type
of the function.– What is the type of the
value that the function computes?
– In other words, what values are legal and illegal for the output of the function?
import java.util.Scanner;
public class example1{ public static double square(double number) { double result = number * number; return result; } public static void main(String[] args) { Scanner in = new Scanner(System.in); System.out.printf("Please enter a number: "); double N = in.nextDouble(); double N_square = square(N); System.out.printf("%.2f squared = %.2f\n", N,
N_square); }}
return type
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How to Write a Function• Specify a name, like
square.• Specify the inputs
(called arguments).• Specify the return type
of the function.• Specify what the
function does. This is what we call the body of the function.
import java.util.Scanner;
public class example1{ public static double square(double number) { double result = number * number; return result; } public static void main(String[] args) { Scanner in = new Scanner(System.in); System.out.printf("Please enter a number: "); double N = in.nextDouble(); double N_square = square(N); System.out.printf("%.2f squared = %.2f\n", N,
N_square); }}
body
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How to Write a Function• Specify a name, like
square.• Specify the inputs
(called arguments).• Specify the return type
of the function.• Specify what the
function does. This is what we call the body of the function.
• Specify what value the function returns, using one or more return statements.
import java.util.Scanner;
public class example1{ public static double square(double number) { double result = number * number; return result; } public static void main(String[] args) { Scanner in = new Scanner(System.in); System.out.printf("Please enter a number: "); double N = in.nextDouble(); double N_square = square(N); System.out.printf("%.2f squared = %.2f\n", N,
N_square); }}
return statement
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Using a Function (Function Calls)• Once you have written
a function, you can use it anywhere in your code, by doing a function call.
import java.util.Scanner;
public class example1{ public static double square(double number) { double result = number * number; return result; } public static void main(String[] args) { Scanner in = new Scanner(System.in); System.out.printf("Please enter a number: "); double N = in.nextDouble(); double N_square = square(N); System.out.printf("%.2f squared = %.2f\n", N,
N_square); }}
function call
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Using a Function (Function Calls)• Once you have written
a function, you can use it anywhere in your code, by doing a function call.
• When you call a function, you must:– Provide the appropriate
argument(s).
import java.util.Scanner;
public class example1{ public static double square(double number) { double result = number * number; return result; } public static void main(String[] args) { Scanner in = new Scanner(System.in); System.out.printf("Please enter a number: "); double N = in.nextDouble(); double N_square = square(N); System.out.printf("%.2f squared = %.2f\n", N,
N_square); }}
argument(s)
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Using a Function (Function Calls)• Once you have written
a function, you can use it anywhere in your code, by doing a function call.
• When you call a function, you must:– Provide the appropriate
argument(s).– Use the return value
appropriately.
import java.util.Scanner;
public class example1{ public static double square(double number) { double result = number * number; return result; } public static void main(String[] args) { Scanner in = new Scanner(System.in); System.out.printf("Please enter a number: "); double N = in.nextDouble(); double N_square = square(N); System.out.printf("%.2f squared = %.2f\n", N,
N_square); }}
storing the return value
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Using the Return Value• In the square function, the
return value is a double.• You can use this value in
any way that you can use any double number. Examples:
• You can store the return value in a variable.
import java.util.Scanner;
public class example1{ public static double square(double number) { double result = number * number; return result; } public static void main(String[] args) { Scanner in = new Scanner(System.in); System.out.printf("Please enter a number: "); double N = in.nextDouble(); double N_square = square(N); System.out.printf("%.2f squared = %.2f\n", N,
N_square); }}
storing the return value in a variable
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Using the Return Value• In the square function, the
return value is a double.• You can use this value in
any way that you can use any double number. Examples:
• You can store the return value in a variable.
• You can print the return value directly.
import java.util.Scanner;
public class example1{ public static double square(double number) { double result = number * number; return result; } public static void main(String[] args) { Scanner in = new Scanner(System.in); System.out.printf("Please enter a number: "); double N = in.nextDouble(); System.out.printf("%.2f squared = %.2f\n", N,
square(N)); }}
printing the return value directly
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Using the Return Value• In the square function, the
return value is a double.• You can use this value in
any way that you can use any double number. Examples:
• You can store the return value in a variable.
• You can print the return value directly.
• You can use it as part of a more complicated expression.
import java.util.Scanner;
public class example1{ public static double square(double number) { double result = number * number; return result; } public static void main(String[] args) { Scanner in = new Scanner(System.in); System.out.printf("Please enter a number: "); double N = in.nextDouble();
double my_var = 18 + square(N); System.out.printf("result = %.2f\n", my_var); }}
using the return value in an expression
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Using the Return Value• In the square function, the
return value is a double.• You can use this value in
any way that you can use any double number. Examples:
• You can store the return value in a variable.
• You can print the return value directly.
• You can use it as part of a more complicated expression.
• You can use it as an argument for another function call.
import java.util.Scanner;
public class example1{ public static double square(double number) { double result = number * number; return result; }
public static void main(String[] args) { Scanner in = new Scanner(System.in); System.out.printf("Please enter a number: "); double N = in.nextDouble();
double my_var = 18 + square(square(N)); System.out.printf("result = %.2f\n", my_var); }}
the return value is used as argument for another function call
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Function Calls
• You can call a function as many times as you like.• On the next slide, we call the square function three
times.
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import java.util.Scanner;
public class example1{ public static double square(double number) { double result = number * number; return result; }
public static void main(String[] args) { Scanner in = new Scanner(System.in); System.out.printf("Please enter a number M: "); double M = in.nextDouble(); System.out.printf("Please enter a number N: "); double N = in.nextDouble();
double M_square = square(M); System.out.printf("%.2f squared = %.2f\n", M, M_square); double N_square = square(N); System.out.printf("%.2f squared = %.2f\n", N, N_square); double MN_square = square(M*N); System.out.printf("%.2f squared = %.2f\n", M*N, M*N_square); }}
Example: Calling the square function three times.
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Example: Printing Prime Numbers• Write a program
that:– Asks the user to
enter an integer N.– Prints all prime
integers from 2 up to (and including) N.
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Example: Printing Prime Numbers• Write a program
that:– Asks the user to
enter an integer N.– Prints all prime
integers from 2 up to (and including) N.
• First step:– Write the basic
structure of the program.
– Put placeholders where more detail is needed.
import java.util.Scanner;
public class example1 { public static void main(String[] args) { Scanner in = new Scanner(System.in); System.out.printf("Enter an integer: "); int N = in.nextInt();
for (int i = 2; i <= N; i++) { if i is prime { System.out.printf("%d\n", i); } } }}
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Example: Printing Prime Numbers• Write a program
that:– Asks the user to
enter an integer N.– Prints all prime
integers from 2 up to (and including) N.
• Second step:– Identify functions
that can be used to complete the program.
import java.util.Scanner;
public class example1 { public static void main(String[] args) { Scanner in = new Scanner(System.in); System.out.printf("Enter an integer: "); int N = in.nextInt();
for (int i = 2; i <= N; i++) { if i is prime { System.out.printf("%d\n", i); } } }}
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Example: Printing Prime Numbers• Write a program
that:– Asks the user to
enter an integer N.– Prints all prime
integers from 2 up to (and including) N.
• We can use a function is_prime to check if i is prime.
• Arguments?
• Return type?
import java.util.Scanner;
public class example1 { public static void main(String[] args) { Scanner in = new Scanner(System.in); System.out.printf("Enter an integer: "); int N = in.nextInt();
for (int i = 2; i <= N; i++) { if i is prime { System.out.printf("%d\n", i); } } }}
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Example: Printing Prime Numbers• Write a program
that:– Asks the user to
enter an integer N.– Prints all prime
integers from 2 up to (and including) N.
• We can use a function is_prime to check if i is prime.
• Arguments? an integer
• Return type? boolean
import java.util.Scanner;
public class example1 { public static void main(String[] args) { Scanner in = new Scanner(System.in); System.out.printf("Enter an integer: "); int N = in.nextInt();
for (int i = 2; i <= N; i++) { if i is prime { System.out.printf("%d\n", i); } } }}
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Example: Printing Prime Numbers• Write a program
that:– Asks the user to
enter an integer N.– Prints all prime
integers from 2 up to (and including) N.
• Step 3: use the function.– We have not written
the function yet, but that is OK.
– Obviously, the program will not run until we write the function.
import java.util.Scanner;
public class example1 { public static void main(String[] args) { Scanner in = new Scanner(System.in); System.out.printf("Enter an integer: "); int N = in.nextInt();
for (int i = 2; i <= N; i++) { if (is_prime(i)) { System.out.printf("%d\n", i); } } }}
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import java.util.Scanner;
public class example1 { public static boolean is_prime(int N) { for (int i = 2; i < N; i++) { if (N % i == 0) { return false; } } return true; } public static void main(String[] args) { Scanner in = new Scanner(System.in); System.out.printf("Enter an integer: "); int N = in.nextInt();
for (int i = 2; i <= N; i++) { if (is_prime(i)) { System.out.printf("%d\n", i); }}}}
• Write a program that:– Asks the user to
enter an integer N.– Prints all prime
integers from 2 up to (and including) N.
• Step 4: write the function.
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Output:
Enter an integer: 802357111317192329313741434753596167717379
import java.util.Scanner;
public class example1 { public static boolean is_prime(int N) { for (int i = 2; i < N; i++) { if (N % i == 0) { return false; } } return true; } public static void main(String[] args) { Scanner in = new Scanner(System.in); System.out.printf("Enter an integer: "); int N = in.nextInt();
for (int i = 2; i <= N; i++) { if (is_prime(i)) { System.out.printf("%d\n", i); }}}}
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Why Do We Need Functions• To write better code:
– More correct, easier to read/write/change.
• To write complicated code.• Functions help us organize code.
YOU CANNOT WRITE NON-TRIVIAL PROGRAMS IF YOU DO NOT USE FUNCTIONS
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Example: Prime Numbers, Again• Write a program that:
– Asks the user to enter an integer N.
– Prints out the smallest prime number greater than or equal to N.
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Example: Prime Numbers, Again• Write a program that:
– Asks the user to enter an integer N.
– Prints out the smallest prime number greater than or equal to N.
• First step:– Write the basic
structure of the program.
– Put placeholders where more detail is needed.
import java.util.Scanner;
public class example1 { public static void main(String[] args) { Scanner in = new Scanner(System.in); System.out.printf("Enter an integer: "); int N = in.nextInt();
int i = N; while (i is not prime) { i++; } System.out.printf("%d\n", i); }}
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Example: Prime Numbers, Again• Write a program that:
– Asks the user to enter an integer N.
– Prints out the smallest prime number greater than or equal to N.
• Second step:– Identify functions that
can be used to complete the program.
• We can use the is_prime function again!!!
import java.util.Scanner;
public class example1 { public static void main(String[] args) { Scanner in = new Scanner(System.in); System.out.printf("Enter an integer: "); int N = in.nextInt();
int i = N; while (is_prime(i) == false) { i++; } System.out.printf("%d\n", i); }}
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• Write a program that:– Asks the user to enter
an integer N.– Prints out the smallest
prime number greater than or equal to N.
• To complete the program, we can just use the is_prime function we already have.
• Functions make it really easy to re-use code!!!
import java.util.Scanner;
public class example1{ public static boolean is_prime(int N) { for (int i = 2; i < N; i++) { if (N % i == 0) { return false; } } return true; }
public static void main(String[] args) { Scanner in = new Scanner(System.in); System.out.printf("Enter an integer: "); int N = in.nextInt(); while (is_prime(N) == false) { N++; } System.out.printf("%d\n", N); }}
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import java.util.Scanner;
public class example1{ public static boolean is_prime(int N) { for (int i = 2; i < N; i++) { if (N % i == 0) { return false; } } return true; }
public static void main(String[] args) { Scanner in = new Scanner(System.in); System.out.printf("Enter an integer: "); int N = in.nextInt(); while (is_prime(N) == false) { N++; } System.out.printf("%d\n", N); }}
Example Output:
Enter an integer: 10000001000003
Example Output:
Enter an integer: 123456789123456791
Example Output:
Enter an integer: 75007507
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Making Code Easier to Read• In lots of programs, we need to perform a task many
times.• Copying and pasting code can work, but has
disadvantages:• The resulting code can look long and ugly.• If we make a mistake, we end up copying and pasting
the mistake many times.– Fixing such mistakes, that have been copied and pasted
many times, can be a pain.
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Example: Input Validation• Write a program that:
– Asks the user to enter integers A, B, C.• if the user enters an invalid input, the program should keep asking
the user to enter a valid integer,
– Prints out the sum of the three integers.
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Example: Input Validation• Write a program that:
– Asks the user to enter integers A, B, C.• if the user enters an invalid input, the program should keep asking
the user to enter a valid integer,
– Prints out the sum of the three integers.
• A first version of the solution can be seen on the next slide.
import java.util.Scanner;public class example1 { public static void main(String[] args) { Scanner in = new Scanner(System.in); int A; while (true) { System.out.printf("Enter integer A: "); String s = in.next(); try { A = Integer.parseInt(s); } catch (Exception e) { System.out.printf("Invalid input\n"); continue; } break; } int B; while (true) { System.out.printf("Enter integer B: "); String s = in.next(); try { B = Integer.parseInt(s); }
catch (Exception e) { System.out.printf("Invalid input\n"); continue; } break; } int C; while (true) { System.out.printf("Enter integer C: "); String s = in.next(); try { C = Integer.parseInt(s); } catch (Exception e) { System.out.printf("Invalid input\n"); continue; } break; } System.out.printf("A + B + C = %d\n", A +
B + C); }}
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Example: Input Validation• Write a program that:
– Asks the user to enter integers A, B, C.• if the user enters an invalid input, the program should keep asking
the user to enter a valid integer,
– Prints out the sum of the three integers.
• A first version of the solution can be seen on the previous slide.
• What is wrong with that code?
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Example: Input Validation• Solution:
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Example: Input Validation• Solution: write a function for getting an integer from
the user.• Name: user_integer• Arguments:
• Return value:
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Example: Input Validation• Solution: write a function for getting an integer from
the user.• Name: user_integer• Arguments:
– One argument - what we print to the user.– Type of the argument: String
• Return value:– int
import java.util.Scanner;
public class example1{ public static int user_integer(String message) { Scanner in = new Scanner(System.in); int result; while (true) { System.out.printf(message); String s = in.next(); try { result = Integer.parseInt(s); } catch (Exception e) { System.out.printf("%s is not a valid integer.\n\n", s); continue; } return result; } }
public static void main(String[] args) { int A = user_integer("Enter integer A: "); int B = user_integer("Enter integer B: "); int C = user_integer("Enter integer C: "); System.out.printf("A + B + C = %d\n", A + B + C); }}
• Here we see a solution that defines and uses the user_integer function.
• The code is shorter.
• Unlike the previous version, code is not duplicated.
• The main function is short and easy to read.
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Example: Repeated Printing• Write a program that:
– Asks the user to enter a string S.– Asks the user to enter a number N.– Prints N times string S.
Enter string S: helloEnter integer N: 5hellohellohellohellohello
Example Output:
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Example: Repeated Printing• Write a program that:
– Asks the user to enter a string S.– Asks the user to enter a number N.– Prints N times string S.
• Let's write a function, that:– takes as input a
string S and an integer N.
– prints the stringN times.
import java.util.Scanner;public class example1{ public static void main(String[] args) { Scanner in = new Scanner(System.in); System.out.printf("Enter string S: "); String S = in.next(); System.out.printf("Enter integer N: "); int N = in.nextInt(); print String S repeatedly, N times. }}
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Example: Repeated Printing• The complete
program is shown on the right.
• Function repeat_print has two features we have not seen before:
• It takes two arguments.
• It returns nothing.
import java.util.Scanner;public class example1{ public static void repeat_print(String message,
int times) { for (int i = 0; i < times; i++) { System.out.printf("%s\n", message); } } public static void main(String[] args) { Scanner in = new Scanner(System.in); System.out.printf("Enter string S: "); String S = in.next(); System.out.printf("Enter integer N: "); int N = in.nextInt(); repeat_print(S, N); }}
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A Function That Returns Nothing• Function repeat_print
does something useful.• However, we do not
want any value returned from the function.
• In that case, we specify the return type of the function as void.
import java.util.Scanner;public class example1{ public static void repeat_print(String message,
int times) { for (int i = 0; i < times; i++) { System.out.printf("%s\n", message); } } public static void main(String[] args) { Scanner in = new Scanner(System.in); System.out.printf("Enter string S: "); String S = in.next(); System.out.printf("Enter integer N: "); int N = in.nextInt(); repeat_print(S, N); }}
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The main Function• When Java executes a program, how does Java know
where to start?• Every program must have a function called main, such
that:– It takes one argument, of type String []. We will understand
this type in our next topic, when we do arrays. – the return type is void.
• Until we saw how to write functions, all our code used to go to main.
• Now that we have started using functions, the main code will be a relatively small part of the program.
• Functions will do the bulk of the work.
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Function Arguments• Functions have arguments.• To call a function XYZ, you write something like :
XYZ(argument_1, …, argument_N)
• How would you know how many arguments to use?
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Function Arguments• Functions have arguments.• To call a function XYZ, you write something like:
XYZ(argument_1, …, argument_N)
• How would you know how many arguments to use?– From the function definition, which (among other things)
defines EXACTLY:• how many arguments to use.• the type of each argument.• the order of the arguments.
public static type XYZ(type 1 arg_1, …, type_N arg_N)
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Executing a Function Call• When the body of the function starts executing, the
only variables visible to the function are:– the arguments.– variables defined in the body of the function.
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What Will This Program Do?public class example1{ public static void foo(String var1,
String var2) { System.out.printf("var1 = %s\n", var1); System.out.printf("var1 = %s\n", var2); } public static void main(String[] args) { String var1 = "hello"; String var2 = "goodbye"; String var3 = "earth"; String var4 = "moon"; foo(var3, var4); System.out.printf("var2 = %s\n", var2); }}
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Step-by-step Execution
Current line
Main Namespace:public class example1{ public static void foo(String var1,
String var2) { System.out.printf("var1 = %s\n", var1); System.out.printf("var1 = %s\n", var2); } public static void main(String[] args) { String var1 = "hello"; String var2 = "goodbye"; String var3 = "earth"; String var4 = "moon"; foo(var3, var4); System.out.printf("var2 = %s\n", var2); }}
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Step-by-step Execution
First line to execute:
variables in main:public class example1{ public static void foo(String var1,
String var2) { System.out.printf("var1 = %s\n", var1); System.out.printf("var1 = %s\n", var2); } public static void main(String[] args) { String var1 = "hello"; String var2 = "goodbye"; String var3 = "earth"; String var4 = "moon"; foo(var3, var4); System.out.printf("var2 = %s\n", var2); }}
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Step-by-step Execution
variables in main:
var1 = "hello"
public class example1{ public static void foo(String var1,
String var2) { System.out.printf("var1 = %s\n", var1); System.out.printf("var1 = %s\n", var2); } public static void main(String[] args) { String var1 = "hello"; String var2 = "goodbye"; String var3 = "earth"; String var4 = "moon"; foo(var3, var4); System.out.printf("var2 = %s\n", var2); }}
First line creates variable var1
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Step-by-step Execution
Next line to execute:
variables in main:
var1 = "hello"
public class example1{ public static void foo(String var1,
String var2) { System.out.printf("var1 = %s\n", var1); System.out.printf("var1 = %s\n", var2); } public static void main(String[] args) { String var1 = "hello"; String var2 = "goodbye"; String var3 = "earth"; String var4 = "moon"; foo(var3, var4); System.out.printf("var2 = %s\n", var2); }}
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Step-by-step Execution
Next line to execute:
variables in main:
var1 = "hello"var2 = goodbye
public class example1{ public static void foo(String var1,
String var2) { System.out.printf("var1 = %s\n", var1); System.out.printf("var1 = %s\n", var2); } public static void main(String[] args) { String var1 = "hello"; String var2 = "goodbye"; String var3 = "earth"; String var4 = "moon"; foo(var3, var4); System.out.printf("var2 = %s\n", var2); }}
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Step-by-step Execution
Next line to execute:
variables in main:
var1 = "hello"var2 = "goodbye"var3 = "earth"
public class example1{ public static void foo(String var1,
String var2) { System.out.printf("var1 = %s\n", var1); System.out.printf("var1 = %s\n", var2); } public static void main(String[] args) { String var1 = "hello"; String var2 = "goodbye"; String var3 = "earth"; String var4 = "moon"; foo(var3, var4); System.out.printf("var2 = %s\n", var2); }}
58
Step-by-step Execution
Next line to execute:function call
variables in main:
var1 = "hello"var2 = "goodbye"var3 = "earth"var4 = "moon"
public class example1{ public static void foo(String var1,
String var2) { System.out.printf("var1 = %s\n", var1); System.out.printf("var1 = %s\n", var2); } public static void main(String[] args) { String var1 = "hello"; String var2 = "goodbye"; String var3 = "earth"; String var4 = "moon"; foo(var3, var4); System.out.printf("var2 = %s\n", var2); }}
59
Step-by-step Execution
Next line to execute:function call.First, assign values to arguments.
variables in main:
var1 = "hello"var2 = "goodbye"var3 = "earth"var4 = "moon"
public class example1{ public static void foo(String var1,
String var2) { System.out.printf("var1 = %s\n", var1); System.out.printf("var1 = %s\n", var2); } public static void main(String[] args) { String var1 = "hello"; String var2 = "goodbye"; String var3 = "earth"; String var4 = "moon"; foo(var3, var4); System.out.printf("var2 = %s\n", var2); }}
variables in foo:
var1 = ???var2 = ???
60
Step-by-step Execution
Next line to execute:function call.First, assign values to arguments.
variables in main:
var1 = "hello"var2 = "goodbye"var3 = "earth"var4 = "moon"
public class example1{ public static void foo(String var1,
String var2) { System.out.printf("var1 = %s\n", var1); System.out.printf("var1 = %s\n", var2); } public static void main(String[] args) { String var1 = "hello"; String var2 = "goodbye"; String var3 = "earth"; String var4 = "moon"; foo(var3, var4); System.out.printf("var2 = %s\n", var2); }}
variables in foo:
var1 = " earth "var2 = " moon "
61
Step-by-step Execution
Next line to execute:How does Java know which var1 to print?
variables in main:
var1 = "hello"var2 = "goodbye"var3 = "earth"var4 = "moon"
public class example1{ public static void foo(String var1,
String var2) { System.out.printf("var1 = %s\n", var1); System.out.printf("var1 = %s\n", var2); } public static void main(String[] args) { String var1 = "hello"; String var2 = "goodbye"; String var3 = "earth"; String var4 = "moon"; foo(var3, var4); System.out.printf("var2 = %s\n", var2); }}
variables in foo:
var1 = " earth "var2 = " moon "
62
Step-by-step Execution
Next line to execute:
variables in main:
var1 = "hello"var2 = "goodbye"var3 = "earth"var4 = "moon"
public class example1{ public static void foo(String var1,
String var2) { System.out.printf("var1 = %s\n", var1); System.out.printf("var1 = %s\n", var2); } public static void main(String[] args) { String var1 = "hello"; String var2 = "goodbye"; String var3 = "earth"; String var4 = "moon"; foo(var3, var4); System.out.printf("var2 = %s\n", var2); }}
variables in foo:
var1 = " earth "var2 = " moon "
Currently executing the body of foo. Only the variables of foo are visible. "hello" is printed.
63
Step-by-step Execution
Next line to execute:
variables in main:
var1 = "hello"var2 = "goodbye"var3 = "earth"var4 = "moon"
public class example1{ public static void foo(String var1,
String var2) { System.out.printf("var1 = %s\n", var1); System.out.printf("var1 = %s\n", var2); } public static void main(String[] args) { String var1 = "hello"; String var2 = "goodbye"; String var3 = "earth"; String var4 = "moon"; foo(var3, var4); System.out.printf("var2 = %s\n", var2); }}
variables in foo:
var1 = " earth "var2 = " moon "
"moon" is printed.
64
Step-by-step Execution
Next line to execute:
variables in main:
var1 = "hello"var2 = "goodbye"var3 = "earth"var4 = "moon"
public class example1{ public static void foo(String var1,
String var2) { System.out.printf("var1 = %s\n", var1); System.out.printf("var1 = %s\n", var2); } public static void main(String[] args) { String var1 = "hello"; String var2 = "goodbye"; String var3 = "earth"; String var4 = "moon"; foo(var3, var4); System.out.printf("var2 = %s\n", var2); }}
variables in foo:
var1 = " earth "var2 = " moon "
Which line comes next?
65
Step-by-step Execution
Next line to execute:
variables in main:
var1 = "hello"var2 = "goodbye"var3 = "earth"var4 = "moon"
public class example1{ public static void foo(String var1,
String var2) { System.out.printf("var1 = %s\n", var1); System.out.printf("var1 = %s\n", var2); } public static void main(String[] args) { String var1 = "hello"; String var2 = "goodbye"; String var3 = "earth"; String var4 = "moon"; foo(var3, var4); System.out.printf("var2 = %s\n", var2); }}
Done with the function call.The variables of foo disappear.
66
Step-by-step Execution
Next line to execute:
variables in main:
var1 = "hello"var2 = "goodbye"var3 = "earth"var4 = "moon"
public class example1{ public static void foo(String var1,
String var2) { System.out.printf("var1 = %s\n", var1); System.out.printf("var1 = %s\n", var2); } public static void main(String[] args) { String var1 = "hello"; String var2 = "goodbye"; String var3 = "earth"; String var4 = "moon"; foo(var3, var4); System.out.printf("var2 = %s\n", var2); }}
"goodbye" is printed.
67
Summary of Program Output
Output:
var1 = "earth"var2 = "moon"var2 = "goodbye"
public class example1{ public static void foo(String var1,
String var2) { System.out.printf("var1 = %s\n", var1); System.out.printf("var1 = %s\n", var2); } public static void main(String[] args) { String var1 = "hello"; String var2 = "goodbye"; String var3 = "earth"; String var4 = "moon"; foo(var3, var4); System.out.printf("var2 = %s\n", var2); }}