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Chapter 2: Elementary Programming

Shahriar Hossain

Quiz solution

What will be the value of the variable x after performing the following Java statement:int x = 7 − 10 % 2 / 3;

Solution: 7

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Consecutive multiplicative operators will be evaluated from left to right in the expression since they have the same priority.

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Quiz solution

What will be printed as a result of the following piece of code? explain step-by-step:double x = 3;

double y = x + 1;

x = y − 2;

System.out.println(x);

System.out.println(y);

Solution:

2.0

4.0

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Objectives To use augmented assignment operators To distinguish between postincrement and

preincrement and between postdecrement and predecrement

To cast the value of one type to another type To represent characters using the char type To represent a string using the String type

To become familiar with Java programming style and documentation

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Declaring Variablesint x; // Declare x to be an // integer variable;

double radius; // Declare radius to // be a double variable;

char a; // Declare a to be a // character variable;

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Assignment Statements

x = 1; // Assign 1 to x;

radius = 1.0; // Assign 1.0 to radius;

a = 'A'; // Assign 'A' to a;

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Numeric Operators

Name Meaning Example Result

+ Addition 34 + 1 35 - Subtraction 34.0 – 0.1 33.9 * Multiplication 300 * 30 9000 / Division 1.0 / 2.0 0.5 % Remainder 20 % 3 2

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Augmented Assignment Operators

Operator Example Equivalent

+= i += 8 i = i + 8

-= f -= 8.0 f = f - 8.0

*= i *= 8 i = i * 8

/= i /= 8 i = i / 8

%= i %= 8 i = i % 8

The operators +, -, *, /, and % can be combined with the assignment operator to form augmented operators.

Caution

There is no spaces in the augmented assignment operators+ = is wrong

+= is correct

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Increment andDecrement Operators

Operator Name Description++var preincrement The expression (++var) increments var by 1

and evaluates to the new value in var after the increment.

var++ postincrement The expression (var++) evaluates to the original value

in var and increments var by 1. --var predecrement The expression (--var) decrements var by 1

and evaluates to the new value in var after the decrement.

var-- postdecrement The expression (var--) evaluates to the original value

in var and decrements var by 1.

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Increment andDecrement Operators, cont.

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Increment andDecrement Operators, cont.

Using increment and decrement operators makes expressions short, but it also makes them complex and difficult to read. Avoid using these operators in expressions that modify multiple variables, or the same variable for multiple times such as this: int k = ++i + i.

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Increment andDecrement Operators, cont.

What is the output of the following code segment?

int i=2;int k=++i+i;System.out.println(i);System.out.println(k);

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Increment andDecrement Operators, cont.

What is the output of the following code segment?

int i=2;int k=i+++i; // equivalent to int k=(i++)+i;System.out.println(i);System.out.println(k);

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Numeric Type Conversion

Consider the following statements:

byte i = 100;

long k = i * 3 + 4;

double d = i * 3.1 + k / 2;

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Conversion RulesWhen performing a binary operation involving two operands of different types, Java automatically converts the operand based on the following rules:

 1.    If one of the operands is double, the other is

converted into double.2.    Otherwise, if one of the operands is float, the other is

converted into float.3.    Otherwise, if one of the operands is long, the other is

converted into long.4.    Otherwise, both operands are converted into int.

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Type CastingImplicit casting double d = 3; (type widening)

Explicit casting int i = (int)3.0; (type narrowing) int i = (int)3.9; (Fraction part is truncated)

What is wrong? int x = 5 / 2.0;The correct statement is int i=(int)(5/2.0);

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Type Casting

byte, short, int, long, float, double

range increases

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Casting in an Augmented Expression

In Java, an augmented expression of the form x1 op= x2 is implemented as x1 = (T)(x1 op x2), where T is the type for x1. Therefore, the following code is correct.

int sum = 0;

sum += 4.5; // sum becomes 4 after this statement

sum += 4.5 is equivalent to sum = (int)(sum + 4.5).

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Character Data Type

char letter = 'A'; (ASCII)

char numChar = '4'; (ASCII)

char letter = '\u0041'; (Unicode)

char numChar = '\u0034'; (Unicode)

Four hexadecimal digits.

NOTE: The increment and decrement operators can also be used on char variables to get the next or preceding Unicode character. For example, the following statements display character b.

char ch = 'a';

System.out.println(++ch);

ASCII (The American Standard Code for Information Interchange)

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Unicode

An encoding scheme established by the Unicode Consortium

Originally 16-bit but there are supplementary characters beyond the 16-bit limit

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Escape Sequences for Special Characters

Description Escape Sequence Unicode

Backspace \b \u0008

Tab \t \u0009

Linefeed \n \u000A

Carriage return \r \u000D

Backslash \\ \u005C

Single Quote \' \u0027

Double Quote \" \u0022

Example

Is this a correct statement?System.out.println("He said "Java is fun" ");

No. The statement above will give a compiler error

The correct statement will beSystem.out.println("He said \"Java is fun\" ");

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