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Methods (Functions)
CSE 1310 – Introduction to Computers and Programming
Vassilis Athitsos
University of Texas at Arlington
1
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.
2
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.
3
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);
}
}
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. 4
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);
}
}
How to Write a Function
• Specify a name, like square.
5
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
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?
6
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);
}
}
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. 7
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)
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?
8
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
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.
9
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
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. 10
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
Using a Function (Function Calls)
• Once you have written a function, you can use it anywhere in your code, by doing a function call.
11
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
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).
12
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)
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.
13
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
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.
14
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
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.
15
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
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.
16
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
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.
17
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
Function Calls
• You can call a function as many times as you like.
• On the next slide, we call the square function three times.
18
19
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.
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.
20
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.
21
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);
}
}
}
}
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.
22
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);
}
}
}
}
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?
23
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);
}
}
}
}
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
24
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);
}
}
}
}
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.
25
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);
}
}
}
}
26
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.
27
Output:
Enter an integer: 80
2
3
5
7
11
13
17
19
23
29
31
37
41
43
47
53
59
61
67
71
73
79
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);
}}}}
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
28
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.
29
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.
30
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);
}
}
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!!!
31
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);
}
}
• 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!!!
32
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);
}
}
33
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: 1000000
1000003
Example Output:
Enter an integer: 123456789
123456791
Example Output:
Enter an integer: 7500
7507
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.
34
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.
35
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.
36
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);
}
}
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?
38
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?
– It is too long.
– It is hard to read and understand.
39
Example: Input Validation
• Solution:
40
Example: Input Validation
• Solution: write a function for getting an integer from the user.
• Name: user_integer
• Arguments:
• Return value:
41
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
42
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.
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.
44
Enter string S: hello
Enter integer N: 5
hello
hello
hello
hello
hello
Example Output:
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 string N times.
45
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.
}
}
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.
46
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);
}
}
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.
47
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);
}
}
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. 48
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?
49
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)
50
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.
51
What Will This Program Do?
52
public class example1
{
public static void foo(String var1,
String var2)
{
System.out.printf("var1 = %s\n", var1);
System.out.printf("var2 = %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);
}
}
Step-by-step Execution
53
Current line
variables in main:
public class example1
{
public static void foo(String var1,
String var2)
{
System.out.printf("var1 = %s\n", var1);
System.out.printf("var2 = %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);
}
}
Step-by-step Execution
54
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("var2 = %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);
}
}
Step-by-step Execution
55
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("var2 = %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
Step-by-step Execution
56
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("var2 = %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);
}
}
Step-by-step Execution
57
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("var2 = %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);
}
}
Step-by-step Execution
58
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("var2 = %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);
}
}
Step-by-step Execution
59
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("var2 = %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);
}
}
Step-by-step Execution
60
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("var2 = %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 = ???
Step-by-step Execution
61
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("var2 = %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"
Step-by-step Execution
62
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("var2 = %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"
Step-by-step Execution
63
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("var2 = %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. “earth" is printed.
Step-by-step Execution
64
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("var2 = %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.
Step-by-step Execution
65
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("var2 = %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?
Step-by-step Execution
66
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("var2 = %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.
Step-by-step Execution
67
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("var2 = %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.
Summary of Program Output
68
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("var2 = %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);
}
}
