Instance Methods in Java

An instance method belongs to an object of a class and requires an instance to be called. It can access and modify the object’s instance variables and can also call other instance or static methods.

• Can access and modify instance variables (object state).
• Can accept parameters and return a value.
• Can call other instance methods or static methods.
• Supports encapsulation and object-oriented design.
• Follows the divide-and-conquer principle in larger applications.

class Person {
    String name = "Alice";

    // Instance method
    void greet()
    {
        System.out.println("Hello, " + name + "!");
    }

    public static void main(String[] args)
    {
        Person p = new Person();
        p.greet(); // Calling instance method
    }
}

Hello, Alice!

Explanation:

• greet() is an instance method.
• It prints the name of the object.
• Called using an object p of the Person class.

Syntax

modifier return_type method_name( )
{
method body ;
}

• modifier: It defines the access type of the method, and it is optional to use.
• return_type:Type of value returned by the method (int, void, String, etc.).
• method_name: Name of the method.
• method body: The method body describes what the method does with statements.

Example: Instance Method With Parameter

import java.io.*;

class GFG{
    
      // static method
    public static void main (String[] args){ 
      
          // creating object
        GFG obj = new GFG();            
      
          // calling instance method by passing value
        obj.add(2,3);    
      
        System.out.println("GFG!");
    }
  
  // Instance method with parameter
  void add(int a, int b){
      
    // local variables
    int x= a;                    
    int y= b;                    
    int z= x + y;             
    
    System.out.println("Sum : " + z);
  }
}

Sum : 5
GFG!

Explanation:

• GFG class has an instance method add() that accepts two integers.
• The method adds the numbers and prints their sum.
• We create an object and call add() with parameters 2 and 3.

Types of Instance Methods:

There are two types of Instance methods in Java:

1. Accessor Methods (Getters)

Getter methods are used to retrieve the value of a private instance variable. They provide controlled access to object data without allowing modification.

class Account {
    private int balance = 100;

    // Accessor method (getter)
    public int getBalance() { return balance; }

    public static void main(String[] args)
    {
        Account acc = new Account();
        System.out.println(
            "Balance: "
            + acc.getBalance()); // Calling getter
    }
}

Balance: 100

Explanation:

• Returns the value of a private instance variable.
• Provides controlled access to the data.

2. Mutator Methods (Setters)

Setter methods are used to modify or update the value of a private instance variable. They allow controlled updates while maintaining encapsulation.

class Account {
    private int balance = 100;

    // Mutator method (setter)
    public void setBalance(int amount)
    {
        balance += amount;
    }

    public int getBalance() { return balance; }

    public static void main(String[] args)
    {
        Account acc = new Account();
        acc.setBalance(50); // Updating balance
        System.out.println(
            "Balance: "
            + acc.getBalance()); // Calling getter
    }
}

Balance: 150

Explanation:

• Modifies the value of a private instance variable.
• Works together with a getter to control access to data.