Java Statements

Understanding different types of statements in Java programming

📋 Java Statements

Java statements are instructions that tell the program what to do. They include variable declarations, assignments, method calls, and control flow statements that execute sequentially. 


// Different types of Java statements
public class StatementExample {
    public static void main(String[] args) {
        int age = 25;                    // Declaration statement
        age = age + 1;                   // Assignment statement
        System.out.println("Age: " + age); // Method call statement
    }
}

Output:

Age: 26

Types of Statements

📝

Declaration

Create variables and constants 

int number;
String name = "John";
➡️

Assignment

Assign values to variables 

number = 42;
name = "Jane";
📞

Method Call

Execute methods and functions 

System.out.println("Hello");
Math.max(10, 20);
🔄

Control Flow

Control program execution 

if (condition) { }
for (int i = 0; i < 10; i++) { }

🔹 Declaration Statements

Declare variables to store data: 

// Variable declarations
int age;                    // Declare integer variable
String name;                // Declare String variable
double salary;              // Declare double variable
boolean isActive;           // Declare boolean variable

// Declaration with initialization
int count = 0;              // Declare and initialize
String message = "Hello";   // Declare and assign value
double price = 99.99;       // Declare with decimal value
boolean found = true;       // Declare with boolean value

// Multiple declarations
int x, y, z;               // Declare multiple variables
int a = 1, b = 2, c = 3;   // Declare and initialize multiple

Example Usage:

Variables declared and ready to use

count = 0, message = "Hello", price = 99.99

🔹 Assignment Statements

Assign values to existing variables: 

public class AssignmentExample {
    public static void main(String[] args) {
        // Simple assignments
        int number = 10;
        number = 20;           // Reassign new value
        number = number + 5;   // Use current value in assignment
        
        // String assignments
        String greeting = "Hello";
        greeting = greeting + " World";  // Concatenation assignment
        
        // Compound assignments (shortcuts)
        int total = 100;
        total += 50;    // Same as: total = total + 50
        total -= 20;    // Same as: total = total - 20
        total *= 2;     // Same as: total = total * 2
        total /= 4;     // Same as: total = total / 4
        
        System.out.println("Number: " + number);
        System.out.println("Greeting: " + greeting);
        System.out.println("Total: " + total);
    }
}

Output:

Number: 35

Greeting: Hello World

Total: 65

🔹 Expression Statements

Statements that evaluate expressions: 

public class ExpressionExample {
    public static void main(String[] args) {
        int a = 10, b = 5;
        
        // Arithmetic expressions
        int sum = a + b;        // Addition
        int difference = a - b; // Subtraction
        int product = a * b;    // Multiplication
        int quotient = a / b;   // Division
        int remainder = a % b;  // Modulus (remainder)
        
        // Increment/Decrement expressions
        a++;    // Post-increment: a = a + 1
        ++b;    // Pre-increment: b = b + 1
        a--;    // Post-decrement: a = a - 1
        --b;    // Pre-decrement: b = b - 1
        
        // Method call expressions
        System.out.println("Sum: " + sum);
        System.out.println("Product: " + product);
        System.out.println("Final a: " + a + ", b: " + b);
    }
}

Output:

Sum: 15

Product: 50

Final a: 10, b: 5

🔹 Block Statements

Group multiple statements together: 

public class BlockExample {
    public static void main(String[] args) {
        int score = 85;
        
        // Block statement with if condition
        if (score >= 80) {
            // This is a block - multiple statements grouped
            System.out.println("Excellent score!");
            String grade = "A";
            System.out.println("Grade: " + grade);
            int bonus = 10;
            System.out.println("Bonus points: " + bonus);
        }
        
        // Block statement with for loop
        System.out.println("Counting:");
        for (int i = 1; i <= 3; i++) {
            // Another block - executed multiple times
            System.out.println("Count: " + i);
            int doubled = i * 2;
            System.out.println("Doubled: " + doubled);
        }
    }
}

Output:

Excellent score!

Grade: A

Bonus points: 10

Counting:

Count: 1

Doubled: 2

Count: 2

Doubled: 4

Count: 3

Doubled: 6

🔹 Empty Statements

Sometimes you need a statement that does nothing: 

public class EmptyStatementExample {
    public static void main(String[] args) {
        int[] numbers = {1, 2, 3, 4, 5};
        int target = 3;
        int index = 0;
        
        // Empty statement in a loop
        // Find index of target number
        while (index < numbers.length && numbers[index] != target) {
            index++;  // Only increment, no other action needed
        }
        
        if (index < numbers.length) {
            System.out.println("Found " + target + " at index " + index);
        } else {
            System.out.println(target + " not found");
        }
        
        // Empty statement with semicolon only
        ; // This is an empty statement - does nothing
    }
}

Output:

Found 3 at index 2

🧠 Test Your Knowledge

What is the correct way to declare and initialize an integer variable?