Chapter 3Fundamental Data Types of Java

Lecture Slides to Accompany

An Introduction to Computer Science Using Java (2nd Edition)

by

S.N. Kamin, D. Mickunas, E. Reingold

Chapter Preview

In this chapter we will:• discuss four important data types

– integers– real numbers– strings– characters

• describe the process of developing and debugging a Java program

Integers

• Numbers without fractional parts

3, 47, -12• Variables can be used to store integers using

an assignment statementint daysInWeek;

daysInWeek = 7;

• In general integer variables may be used any place an integer literal can be

Reading Integers

import CSLib.*;

Inputbox in;

int i;

in = newInputBox();

in.setPrompt(“Enter an integer: “);

i = in.readInt();

Integer Arithmetic Operations

Symbol Operation Example

+ Addition 45 + 5 = 50

- Subtraction 657 – 57 = 600

* Multiplication 7000 * 3 = 2100

/ Division 10 / 3 = 3

% Remainder 10 % 3 = 1

Precedence Rules

1. Evaluate all subexpressions in parentheses2. Evaluate nested parentheses from the

inside out3. In the absence of parentheses or within

parenthesesa. Evaluate *, /, or % before + or –b. Evaluate sequences of *, /, and % operators

from left to rightc. Evaluate sequences of + and – operators from

left to right

Precedence Examples

• Example 16 + 37 % 8 / 5 is the same as6 + ((37 % 8) / 5) = 6 + ( 5 / 5) = 7

• Example 26 + 37 % (8 / 5) =6 + 37 % 1 =6 + 0 = 6

Additional Integer Operators

• Self-assignmenttemperature = temperature + 10;

• Increment cent++; equivalent to cent = cent + 1;

• Decrement cent--; equivalent to cent = cent - 1;

Initializers

• May be used to give variables initial valuesint x = 5;int y = 6;

• Can be written more conciselyint x = 5, y = 6;

• Can use expressions on the right hand sideint x = 5, y = x + 1;

Symbolic Constants

• Useful when you want a variable whose value never changes

• Use the modifier final in its declaration

• Examplefinal int US_Population = 278058881;

Real Numbers

• Numbers with fractional parts

3.14159, 7.12, 9.0, 0.5e001, -16.3e+002• Declared using the type double

double pricePerPound = 3.99;

taxRate = 0.05;

shippingCost = 5.55;

• The initialization part of the declaration is optional

Real Arithmetic Operations

Symbol Operation Example

+ Addition 4.50e01 + 5.30e00 = 5.03e01

- Subtraction 6.57e02 – 5.7oe01 = 6.00e02

* Multiplication 7e02 * 3.0e00 =

2.1e04

/ Division 9.6e01 / 2e01 =

4.8e00

Reading Real Numbers

import CSLib.*;

Inputbox in;

double temp;

in = newInputBox();

in.setPrompt(“Enter a real number: “);

temp = in.readDouble();

Strings

• String is a class defined in the java.lang package

• Unlike other Java classes String has literals and a defined operation

• ExamplesString prompt = “Enter an integer:”;

String t1 = “To be “,

t2 = “or not to be”;

out.print(t1 + t2);

Out.print(“Mass is “ + x * 2.2 + “ Kg”);

String Method Examples

OutputBox out = new OutputBox();String s1 = “Here is a test string”;

out.println(s1.indexOf(“s”)); // prints 6out.println(s1.indexOf(“x”)); // prints -1

out.println(s1.length()); // prints 22

out.println(s1.substring(8,14)); // prints ‘a test’

Reading Strings

import CSLib.*;

Inputbox in;

String input;

in = newInputBox();

in.setPrompt(“Enter a real number: “);

input = in.readString();

Characters

• Any key you type on the keyboard generates a character which may or may not be displayed on the screen (e.g. nonprinting characters)

• Characters are a primitive type in Java and are not equivalent to strings

• Exampleschar vitamin = ‘’A’, chromosome = ‘’y’, middleInitial = ‘’N’;

Important Literal Characters

‘A’, … ,‘Z’ Uppercase letters

‘a’, … ,‘z’ Lowercase letters

‘0’, … , ‘9’ Digits

‘.’,’,’,’!’,’”’,etc. Punctuation Marks

‘ ’ Blank

‘\n’ New line

‘\t’ Tab

‘\\’ Backslash

‘\’’ Single Right Quote

Common Debugging Problems

• Misleading compiler error messages– Syntax errors indicated on one-line may actually

reflect an error made on an earlier line

• Capitalization errors– Java is case sensitive, identifier names must use

the same capitalization rules each time

• Logic Errors– Program appears to run correctly, but on closer

inspection the wrong output is displayed

Limitations of Numeric Variables

• Unlike the integers mathematics the type int is not infinitely large and it is possible to compute a value incorrectly because the value is too large to be stored in an int variable storage location

• Unlike the real numbers in mathematics the type double is not dense, it is not always possible to test double expressions for equality and obtain a correct result due to rounding errors in representations

Mixing Numeric Data Types

• Java will automatically convert int expressions to double values without loss of information

int i = 5;

double x = i + 10.5;• To convert double expressions to int requires a

typecasting operation and truncation will occuri = (int) (10.3 * x)

• To round-up instead of truncating add 0.5i = (int) (10.3 * x + 0.5)

Mixed Mode Operations and Strings

• It is important to remember that “13” and 13 are not the same

• Examplesout.println(“4” + “5”) // prints 45

out.println(“4” + 5) // prints 45

out.println(4 + 5) // prints 9

Characters as Integers

• It is legal to assign a char to an int variable

int i = ‘a’; // assigns 97 to i• It is legal to assign an int to an char variable

char c = 97; // assigns ‘a’ to c• It is possible to perform arithmetic on char

variables

char ch = ‘a’;

ch = ch + 1; // assigns ‘b’ to ch