Operators#

Introduction#

In Java, operators are symbols used to perform operations on values and variables.

What Is an Operator?#

An operator is a symbol that tells Java to perform a particular operation.

For example:

int result = 10 + 20;

Here:

• 10 → operand
• 20 → operand
• + → operator
• result → variable storing the result

The values on which an operator works are called operands.

---

Types of Operators in Java#

Java operators can be classified as:

Operators
├── Arithmetic Operators
├── Assignment Operators
├── Relational Operators
├── Logical Operators
├── Unary Operators
├── Ternary Operator
├── Bitwise Operators
├── Shift Operators
└── instanceof Operator

Let's understand them one by one.

---

Arithmetic Operators#

Arithmetic operators are used to perform mathematical operations.

Operator	Meaning	Example
+	Addition	a + b
-	Subtraction	a - b
*	Multiplication	a * b
/	Division	a / b
%	Modulus	a % b

Example:

int a = 10;
int b = 3;

System.out.println(a + b);
System.out.println(a - b);
System.out.println(a * b);
System.out.println(a / b);
System.out.println(a % b);

Output:

13
7
30
3
1

Addition with Strings#

The + operator can also be used to join strings.

String firstName = "Ravi";
String lastName = "Kumar";

String fullName = firstName + " " + lastName;

System.out.println(fullName);

Output:

Ravi Kumar

The + operator behaves differently when strings are involved.

For example:

System.out.println("Age: " + 20);

Output:

Age: 20

---

Assignment Operators#

Assignment operators are used to assign values to variables.

The basic assignment operator is:

=

Example:

int x = 10;

Here, 10 is assigned to x.

Java also provides compound assignment operators.

Operator	Example	Equivalent
=	x = 10	x = 10
+=	x += 5	x = x + 5
-=	x -= 5	x = x - 5
*=	x *= 5	x = x * 5
/=	x /= 5	x = x / 5
%=	x %= 5	x = x % 5

---

Relational Operators#

Relational operators are used to compare two values.

The result of a relational operation is a boolean value:

true

or:

false

Operator	Meaning
==	Equal to
!=	Not equal to
>	Greater than
<	Less than
>=	Greater than or equal to
<=	Less than or equal to

Example:

int a = 10;
int b = 20;

System.out.println(a == b);
System.out.println(a != b);
System.out.println(a > b);
System.out.println(a < b);

Output:

false
true
false
true

---

Logical Operators#

Logical operators are used to combine boolean expressions.

Operator	Meaning
&&	Logical AND
`
!	Logical NOT

---

Logical AND &&

The && operator returns true only when both conditions are true.

Condition 1	Condition 2	Result
true	true	true
true	false	false
false	true	false
false	false	false

Example:

int age = 20;

System.out.println(age >= 18 && age <= 60);

Output:

true

Both conditions are true.

---

Logical OR ||

The || operator returns true when at least one condition is true.

Condition 1	Condition 2	Result
true	true	true
true	false	true
false	true	true
false	false	false

Example:

int age = 16;

System.out.println(age < 18 || age > 60);

Output:

true

At least one condition is true.

---

Logical NOT !

The ! operator reverses a boolean value.

boolean passed = true;

System.out.println(!passed);

Output:

false

---

Unary Operators#

Unary operators work with only one operand.

Common unary operators are:

+
-
++
--
!

Example:

int x = 10;

System.out.println(-x);

Output:

-10

The unary minus changes the sign of the value.

Pre-Increment

When ++ is placed before the variable, it is called pre-increment.

int x = 10;

int result = ++x;

System.out.println(x);
System.out.println(result);

Output:

11
11

First x is increased, then its value is used.

Post-Increment

When ++ is placed after the variable, it is called post-increment.

int x = 10;

int result = x++;

System.out.println(x);
System.out.println(result);

Output:

11
10

The current value is used first, and then x is increased.

Pre-Decrement

int x = 10;

int result = --x;

System.out.println(x);
System.out.println(result);

Output:

9
9

---

Post-Decrement

int x = 10;

int result = x--;

System.out.println(x);
System.out.println(result);

Output:

9
10

---

Ternary Operator#

The ternary operator is a short form of a simple if-else statement.

Syntax:

condition ? valueIfTrue : valueIfFalse

Example:

int age = 20;

String result = age >= 18 ? "Adult" : "Minor";

System.out.println(result);

Output:

Adult

The same logic using if-else would be:

int age = 20;
String result;

if (age >= 18) {
    result = "Adult";
} else {
    result = "Minor";
}

The ternary operator is useful when the logic is simple.

---

Bitwise Operators#

Bitwise operators work at the bit level.

Common bitwise operators are:

Operator	Meaning
&	Bitwise AND
`	`
^	Bitwise XOR
~	Bitwise complement

For example:

int a = 5;
int b = 3;

System.out.println(a & b);

The binary values are:

5 = 0101
3 = 0011

Bitwise AND:

0101
0011
----
0001

Output:

1

Bitwise operators are commonly used in low-level programming and specialized applications.

---

Shift Operators#

Shift operators move bits to the left or right.

Operator	Meaning
<<	Left shift
>>	Right shift
>>>	Unsigned right shift

Example:

int x = 5;

System.out.println(x << 1);

Output:

10

Another example:

int x = 8;

System.out.println(x >> 1);

Output:

4

---

instanceof Operator#

The instanceof operator is used to check whether an object belongs to a particular type.

Example:

String name = "Ravi";

System.out.println(name instanceof String);

Output:

true

The result is a boolean value.

---

Conditional Statements#

Introduction#

In a Java program, sometimes we need to make decisions.

For example:

• If a student passes, display "Pass".
• If the age is 18 or above, allow the user to vote.
  For these situations, Java provides conditional statements.

Conditional statements allow a program to execute different blocks of code depending on whether a condition is true or false.

What Is a Conditional Statement?#

A conditional statement checks a condition and decides which code should execute.

For example:

int age = 20;

if (age >= 18) {
    System.out.println("Eligible");
}

Here:

age >= 18

is the condition.

Because the condition is true, the message is printed.

---

Types of Conditional Statements#

Java provides several ways to make decisions.

Conditional Statements
├── if
├── if-else
├── else-if
├── Nested if 
└── switch

Let's understand each one.

if Statement#

The if statement executes a block of code only when the condition is true.

Syntax:

if (condition) {
    // statements
}

Example:

int age = 20;

if (age >= 18) {
    System.out.println("You are an adult");
}

Output:

You are an adult

Because age >= 18 is true.

If the condition is false, the statements inside the if block are skipped.

For example:

int number = -10;

if (number > 0) {
    System.out.println("Positive number");
}

There is no output because the condition is false.

---

if-else Statement#

The if-else statement provides two choices.

If the condition is true, the if block executes.

If the condition is false, the else block executes.

Syntax:

if (condition) {
    // if block
} else {
    // else block
}

Example:

int age = 16;

if (age >= 18) {
    System.out.println("Eligible");
} else {
    System.out.println("Not eligible");
}

Output:

Not eligible

---

else-if Statement#

When there are multiple conditions, we can use else-if.

Syntax:

if (condition1) {

} else if (condition2) {

} else if (condition3) {

} else {

}

Example:

int marks = 85;

if (marks >= 90) {
    System.out.println("Grade A");
} else if (marks >= 75) {
    System.out.println("Grade B");
} else if (marks >= 60) {
    System.out.println("Grade C");
} else if (marks >= 40) {
    System.out.println("Grade D");
} else {
    System.out.println("Fail");
}

Output:

Grade B

Java checks the conditions from top to bottom.

As soon as one condition becomes true, its block executes and the remaining conditions are skipped.

---

Nested if#

An if statement inside another if statement is called a nested if.

Example:

int age = 20;
boolean hasId = true;

if (age >= 18) {

    if (hasId) {
        System.out.println("Entry allowed");
    }
}

Output:

Entry allowed

Here, the second condition is checked only when the first condition is true.

---

switch Statement#

The switch statement is useful when we want to compare one value against multiple possible values.

Syntax:

switch (expression) {

    case value1:
        // statements
        break;

    case value2:
        // statements
        break;

    default:
        // statements
}

Example:

int day = 2;

switch (day) {

    case 1:
        System.out.println("Monday");
        break;

    case 2:
        System.out.println("Tuesday");
        break;

    case 3:
        System.out.println("Wednesday");
        break;

    default:
        System.out.println("Invalid day");
}

Output:

Tuesday

---

if-else vs switch#

Both can be used for decision-making, but they are commonly used in different situations.

if-else	switch
Useful for conditions and ranges	Useful for matching specific values
Supports complex boolean expressions	Commonly compares one expression with cases
Can use >, <, >=, &&, `
Good for ranges	Good for fixed choices

---

Loops#

Introduction#

Sometimes we need to execute the same block of code multiple times.

For example:

• Print numbers from 1 to 10
• Print a message 5 times
• Calculate the sum of numbers

Writing the same statement again and again would make the program long and difficult to maintain.

For example:

System.out.println(1);
System.out.println(2);
System.out.println(3);
System.out.println(4);
System.out.println(5);

Instead, Java provides loops.

A loop allows us to execute a block of code repeatedly.

What Is a Loop?#

A loop is a programming structure used to execute a block of code repeatedly while a condition is satisfied.

For example:

int i = 1;

while (i <= 5) {

    System.out.println(i);

    i++;
}

Output:

1
2
3
4
5

Instead of writing five println() statements, we used a loop.

---

Types of Loops in Java#

Java provides several types of loops.

Loops
├── while loop
├── do-while loop
├── for loop
└── enhanced for loop

We also use:

• Nested loops
• break
• continue

Let's understand them one by one.

---

while Loop#

The while loop executes a block of code as long as the condition is true.

Syntax:

while (condition) {
    // statements
}

Example:

int i = 1;

while (i <= 5) {

    System.out.println(i);

    i++;
}

Output:

1
2
3
4
5

---

do-while Loop#

The do-while loop is similar to the while loop.

The important difference is:

A do-while loop executes its body at least once.

Syntax:

do {
    // statements
} while (condition);

Example:

int i = 1;

do {

    System.out.println(i);

    i++;

} while (i <= 5);

Output:

1
2
3
4
5

---

while vs do-while

Consider this example.

while#

int i = 10;

while (i <= 5) {

    System.out.println(i);
}

There is no output because the condition is false before the first execution.

do-while#

int i = 10;

do {

    System.out.println(i);

} while (i <= 5);

Output:

10

Why?

Because the do block executes first.

Only after that does Java check the condition.

---

for Loop#

The for loop is commonly used when we know how many times we want to repeat something.

Syntax:

for (initialization; condition; update) {
    // statements
}

Example:

for (int i = 1; i <= 5; i++) {

    System.out.println(i);
}

Output:

1
2
3
4
5

---

Enhanced for Loop#

Java also provides an enhanced for loop.

It is commonly used to iterate through arrays and collections.

Syntax:

for (dataType variable : array) {
    // statements
}

Example:

int[] numbers = {10, 20, 30, 40, 50};

for (int number : numbers) {

    System.out.println(number);
}

Output:

10
20
30
40
50

The enhanced for loop is also called the for-each loop.

---

Nested Loops#

A loop inside another loop is called a nested loop.

Example:

for (int i = 1; i <= 3; i++) {

    for (int j = 1; j <= 3; j++) {

        System.out.println(i + " " + j);
    }
}

Output:

1 1
1 2
1 3
2 1
2 2
2 3
3 1
3 2
3 3

The inner loop executes completely for every iteration of the outer loop.

---

Example: Printing a Pattern

Nested loops are commonly used to create patterns.

for (int i = 1; i <= 5; i++) {

    for (int j = 1; j <= i; j++) {

        System.out.print("* ");
    }

    System.out.println();
}

Output:

* 
* * 
* * * 
* * * * 
* * * * * 

---

break Statement#

The break statement is used to immediately terminate a loop.

Example:

for (int i = 1; i <= 10; i++) {

    if (i == 5) {
        break;
    }

    System.out.println(i);
}

Output:

1
2
3
4

When i becomes 5, the break statement ends the loop.

---

continue Statement#

The continue statement skips the current iteration and moves to the next iteration.

Example:

for (int i = 1; i <= 5; i++) {

    if (i == 3) {
        continue;
    }

    System.out.println(i);
}

Output:

1
2
4
5

The value 3 is skipped.

---

break vs continue#

break	continue
Terminates the loop	Skips current iteration
Loop ends immediately	Loop continues
Used when we want to stop	Used when we want to skip

Example:

break;

means:

Stop the loop.

Example:

continue;

means:

Skip this iteration and continue with the next one.

---

Infinite Loop#

An infinite loop is a loop that never ends because its condition never becomes false.

Example:

while (true) {

    System.out.println("Hello");
}

This loop continues forever unless something interrupts the program.

Another example:

for (;;) {

    System.out.println("Hello");
}

An infinite loop can sometimes be intentional, but an accidental infinite loop is usually a programming mistake.

---

while vs do-while vs for

Feature	while	do-while	for
Condition checked	Before execution	After execution	Before execution
Minimum executions	0	1	0
Common use	Unknown number of iterations	At least one execution required	Known/repeated count
Syntax	Simple	Simple	Initialization + condition + update

---

Which Loop Should You Use?#

A simple way to remember:

Use for

When you generally know how many times the loop should execute.

Use while

When the number of iterations may depend on a condition.

Use do-while

When the code should execute at least once.

Use Enhanced for

When you want to iterate through an array or collection.

---

Check Your Understanding#

1. Write a Java program to print numbers from 1 to 20 and check whether each number is Even or Odd using a loop and if-else.

2. Write a Java program to take three numbers from the user and find the largest number using operators and conditional statements.

3. Write a Java program to print all numbers from 1 to 100 that are divisible by both 3 and 5.