Chapter 2: Java Fundamentals

Chapter 2: Java Fundamentals

Operators

Content

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Group of Operators Arithmetic Operators Assignment Operator Order of Precedence Increment/Decrement Operators Relational Operators Logical Operators Operator precedence Casting

Operators

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Operators are special symbols used for: mathematical functions assignment statements logical comparisons

Examples of operators: 3 + 5 // uses + operator 14 + 5 – 4 * (5 – 3) // uses +, -, * operators

Expressions: can be combinations of variables and operators that result in a value

Groups of Operators

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There are 5 different groups of operators: Arithmetic Operators Assignment Operator Increment / Decrement Operators Relational Operators Logical Operators

Java Arithmetic Operators

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Addition +Subtraction –Multiplication Division /Remainder (modulus ) %

Arithmetic Operators

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The following table summarizes the arithmetic operators available in Java.

This is an integer division where the fractional part is truncated.

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Example

Example of division issues:

10 / 3 gives 3

10.0 / 3 gives 3.33333

As we can see, • if we divide two integers we get an integer result.

• if one or both operands is a floating-point value we get a floating-point result.

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Modulus

Generates the remainder when you divide two integer values.

5%3 gives 2 5%4 gives 1

5%5 gives 0 5%10 gives 5

Modulus operator is most commonly used with integer operands. If we attempt to use the modulus operator on floating-point values we will garbage!

Order of Precedence

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( ) evaluated first, inside-out

, /, or % evaluated second, left-to-right

+, evaluated last, left-to-right

Basic Assignment Operator

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We assign a value to a variable using the basic assignment operator (=).

Assignment operator stores a value in memory. The syntax is

leftSide = rightSide ;

Examples:i = 1;

start = i;

sum = firstNumber + secondNumber;avg = (one + two + three) / 3;

Allways it is a variable identifier.

It is either a literal | a variable identifier | an expression.

The Right Side of the Assignment Operator

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The Java assignment operator assigns the value on the right side of the operator to the variable appearing on the left side of the operator.

The right side may be either: Literal: ex. i = 1; Variable identifier: ex. start = i; Expression: ex. sum = first + second;

Assigning Literals

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In this case, the literal is stored in the space memory allocated for the variable at the left side.

int firstNumber=1, secondNumber;firstNumber = 234;secondNumber = 87;

A

B

firstNumber 1

secondNumber ???

A. Variables are allocated in memory.


B. Literals are assigned to variables.

B. Literals are assigned to variables.

firstNumber 234

secondNumber 87Code

State of Memory

Assigning Variables

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In this case, the value of the variable at the right side is stored in the space memory allocated for the variable at the left side.

int firstNumber=1, i;firstNumber = 234;i = firstNumber;

A

B

firstNumber 1

i ???



B. values are assigned to variables.

B. values are assigned to variables.

firstNumber 234

i 234Code

State of Memory

Assigning Expressions

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In this case, the result of the evaluation of the expression is stored in the space memory allocated for variable at the left side.

int first, second, sum;first = 234;second = 87;Sum = first + second

A

B



B. Values are assigned to variables.

B. Values are assigned to variables.

Code

State of Memory

first 1 second ???

sum ???

first 234 second 87

sum 321

Updating Data

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Code State of Memory

number ???

A. The variable is allocated in memory.

A. The variable is allocated in memory.

B. The value 237 is assigned to number.

B. The value 237 is assigned to number.

int number;

number = 237;

AB

Cnumber = 35;C. The value 35

overwrites the previous value 237.

C. The value 35 overwrites the

previous value 237.

number 237

number 35

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public class Sum { // main method public static void main( String args[] ){ int a, b, sum; a = 20;

b = 10; sum = a + b; System.out.println(a + ” + ” + b + “ = “ + sum);

} // end main } // end class Sum

Example: Sum of two integer

Arithmetic/Assignment Operators

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Java allows combining arithmetic and assignment operators into a single operator:

Addition/assignment +=Subtraction/assignment =Multiplication/assignment =Division/assignment /=Remainder/assignment %=

Arithmetic/Assignment Operators

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The syntax isleftSide Op= rightSide ;

This is equivalent to:leftSide = leftSide Op rightSide ;

x%=5; x = x % 5; x*=y+w*z; x = x*(y+w*z);

Allways it is a variable identifier. It is an arithmetic

operator.

It is either a literal | a variable identifier | an expression.

Increment/Decrement Operators

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Only use ++ or when a variable is being incremented/decremented as a statement by itself.

x++; is equivalent to x = x+1;

x--; is equivalent to x = x-1;

Pre-increment versus post-increment

If the unary increment operator, ++, is used after the operand, e.g. x++, it is called a postincrement operator.

If the unary increment operator, ++, is used before the operand, e.g. ++x, it is called a preincrement operator.

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It is important to note that when incrementing or decrementing a variable in a statement by itself, there is no difference between the pre and post forms of the operator.

It is only when a variable occurs in the context of a larger expression, that the pre and post forms of the operator have a different effect.

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if we include the statement ++x as part of a larger statement, e.g.y = ++x;

the effect is :

The value in x is incremented.The new value x is stored in y.

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x = 5;y = ++x;

After these statements are executed, x contains the value ?.y contains the value ?.

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x = 5;y = ++x;

After these statements are executed, x contains the value 6.y contains the value 6.

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However, if we include the statement x++ as part of a larger statement, e.g.y = x++;

the effect is somewhat different.

The old value of x is stored in y. The value in x is incremented

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x = 5;y = x++;

After these statements are executed, x contains the value ?.y contains the value ?.

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x = 5;y = x++;

After these statements are executed, x contains the value 6.y contains the value 5.

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int z = 2;

System.out.println(z);

System.out.println(z++);


System.out.println();

z = 2;


System.out.println(++z);


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The output from this code would be:

2

2

3

2

3

3

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If the unary increment operator, ++, is used after the operand, e.g. x++, it is called a postincrement operator.

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The unary decrement operator, −−, also has two forms:postdecrement, x−−predecrement, −−x

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The unary decrement operator, −−, also has two forms:postdecrement, x−−predecrement, −−x

The difference between the postdecrement and predecrement operators is the same as the difference between the postincrement and preincrement operators.

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It is important to note that when incrementing or decrementing a variable in a statement by itself, there is no difference between the pre and post forms of the operator.

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Increment the value in the integer variable x by 1 in four different ways.

1.x = x+1;

2.++x;

3.x++;

4.x += 1;

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What is the value in i and n after the following code snippet has been executed?

int i=10;

int n = i++ % 5;

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What is the value in i and n after the following code snippet has been executed?

int i=10;

int n = i++ % 5;

i has the value 11.

n has the value 0.

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What would be the effect of changing the postincrement operator to a preincrement operator?

int i=10;

int n = ++i % 5;

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What would be the effect of changing the postincrement operator to a preincrement operator?

int i=10;

int n = ++i % 5;

i has the value 11;

n has the value 1;

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Relational Operators

Relational operators compare two values They Produce a boolean value (true or false)

depending on the relationship

Operation

Is true when

a >b a is greater than b

a >=b a is greater than or equal to b

a ==b a is equal to b

a !=b a is not equal to b

a <=b a is less than or equal to b

a <b a is less than b

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Example

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int x = 3; int y = 5; boolean result;

result = (x > y); now result is assigned the value false

because 3 is not greater than 5

Logical Operators

Symbol Name&& AND

|| OR

! NOT

|| T F

T T T

F T F

&& T F

T T F

F F F

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Example

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boolean x = true;boolean y = false;boolean result;

result = (x && y);result is assigned the value false

result = ((x || y) && x);(x || y) evaluates to true(true && x) evaluates to trueresult is then assigned the value true

Operators Precedence

Parentheses (), inside-out

Increment/decrement ++, --, from left to right

Multiplicative *, /, %, from left to right

Additive +, -, from left to right

Relational <, >, <=, >=, from left to right

Equality ==, !=, from left to right

Logical AND &&

Logical OR ||

Assignment =, +=, -=, *=, /=, %=

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Type Conversion (Casting)

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Used: to change one data type to another . to avoid implicit type coercion.

Syntax:

(dataTypeName) expression

Expression evaluated first, then the value is converted to dataTypeName


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Examples:1. (int)(7.9 + 6.7) -> 142. (int)(7.9) + (int)(6.7) -> 133. (double)(17) -> 17.04. (double)(8+3) > (double)11 ->11.05. (double)(7) /2 = 7.0/2 -> 3.56. (double)(7/2) = 3.07. (int)(7.8+(double)(15)/2) ->

(int)15.3 ->15

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8. (int)(‘A’) -> 65 9. (int)(‘8’) -> 5610. (char)(65) -> ‘A’ 11. (char)(56) -> ‘8’

Example -TRACE

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This example further illustrates how assignment statements and input statements manipulate variables. Consider the following declarations:

int firstNum;int secondNum;char ch;double z;Also suppose that the following statements execute in the order given:1. firstNum = 4;2. secondNum = 2 * firstNum + 6;3. z = (firstNum + 1) / 2.0;4. ch = 'A';5. firstNum = (int)(z) + 8;6. firstNum = secondNum-- ;

After statment 6 Variables

firstNumsecondNum

ch z

Data type compatibility

int x= 7.5; int x = false; int y=13

double z= y/2; double z =13.0;

int w=z/2;

double z= (double)y/2;

double w=z/2;int w = (int) z/2;

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Implicit VS Explicit type conversions

An implicit conversion is where the conversion happens without any syntax.

e.g.

int i = 999999999;

double d = i;

int x;

char c='a';x=c;

double>int>long>short>byte double>int>long>char

An explicit conversion is where you use some syntax to tell the program to do a conversion.

e.g.

int x=97; char c=(char)x;

int i = 999999999; byte b = (byte) i;

int y=(int)7.5;

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Implicit type conversions Explicit type conversions

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Chapter 2: Java Fundamentals