Methods

A method is a block of code used to perform a specific task.

It helps in code reusability.

java

void greet() {
    System.out.println("Hello");
}

Important Points

A method cannot be declared inside another method or block
Memory is allocated in Stack Area (Stack Frame)
Memory is created when method is called and destroyed after execution

Method Syntax

java

<Access Modifier> <Return Type> <Method Name>(Parameters) {
    // statements
}

1. Access Modifier

Defines scope (where method can be accessed)
public
private
protected
default

2. Return Type

Defines what type of value method returns

Primitive → int, float, etc.
Object → String, custom class
Array
void → no return

🔍 Important Rules:

return statement sends value back to caller
Return value must match return type
return should be last statement

3. Method Name

A valid Java identifier
Used to identify method

4. Parameters

Used to pass input values to method
Optional

Rules for Method Calling:

Argument type must match parameter type
Number of arguments must match
Order must match

Parameter = local variable inside method

java

class Method {
    
    void m1() {
        System.out.println("m1 method");
    }

    int m2() {
        return 10 + 20;
    }

    float average(float n1, float n2) {
        return (n1 + n2) / 2;
    }
}

class Main {
    public static void main(String[] args) {
        
        Method obj = new Method();

        obj.m1();

        int result = obj.m2();
        System.out.println("Result: " + result);

        float avg = obj.average(10.5f, 20.5f);
        System.out.println("Average: " + avg);
    }
}

Types of Methods

1. Instance Method (Non-Static)

Method without static keyword

Works on object (late binding)
Must create object to call method
Can access:
- Instance variables
- Static variables

java

class A {

    int a = 10;
    static int b = 20;

    void m1() {
        System.out.println(a);
        System.out.println(b);
    }
}

class Main {
    public static void main(String[] args) {
        A obj = new A();
        obj.m1();
    }
}

Important:

java

A obj = null;
obj.m1(); // ❌ NullPointerException

2. Static Method

Method declared with static keyword

Key Points:

Works on class level (early binding)
No need to create object
Can directly access:
- Static variables ✅
- Instance variables ❌ (need object)

java

class A {

    int a = 10;
    static int b = 20;

    static void m1() {
        System.out.println("Static method");
        System.out.println(b);
    }
}

class Main {
    public static void main(String[] args) {
        A.m1();
    }
}

Ways to Call Static Method

Using class name (Best practice)

java

A.m1();

Using null reference

java

A a = null;
a.m1();

Using object

java

A a = new A();
a.m1();

Method Memory Management

Methods use Stack Memory
Each method gets a stack frame
Stack works on LIFO (Last In First Out)

(Method Chaining):

plaintext

class A {

    void m1() {
        System.out.println("Start m1");
        m2();
        System.out.println("End m1");
    }

    void m2() {
        System.out.println("Start m2");
        m3();
        System.out.println("End m2");
    }

    void m3() {
        System.out.println("m3 method");
    }
}

class Main {
    public static void main(String[] args) {
        new A().m1();
    }
}

Output:

java

Start m1
Start m2
m3 method
End m2
End m1

Execution Flow:

main() → calls m1()
m1() → calls m2()
m2() → calls m3()
Stack follows LIFO order