Methods in Classes

Intermediate ~15 min read

Methods define the behavior of objects. While fields store data (state), methods perform actions (behavior).

Defining Methods

A method definition looks like this:

public class Car {
    // Field
    int speed = 0;

    // Method
    public void accelerate() {
        speed += 10;
        System.out.println("Speed is now " + speed);
    }
}

Calling Methods

To use a method, you must first create an instance (object) of the class, then use the dot . operator.

Car myCar = new Car();
myCar.accelerate(); // Calls the method

Full Example

public class Calculator {
    double num1;
    double num2;
    
    // Instance method - operates on instance variables
    double add() {
        return num1 + num2;
    }
    
    // Instance method with parameters
    double multiply(double a, double b) {
        return a * b;
    }
    
    // Method that accepts an object as parameter
    void copyFrom(Calculator other) {
        this.num1 = other.num1;
        this.num2 = other.num2;
    }
    
    // Method that returns an object
    Calculator createCopy() {
        Calculator copy = new Calculator();
        copy.num1 = this.num1;
        copy.num2 = this.num2;
        return copy;
    }
    
    void display() {
        System.out.println("num1: " + num1 + ", num2: " + num2);
    }
}

public class OopMethods {
    public static void main(String[] args) {
        Calculator calc1 = new Calculator();
        calc1.num1 = 10;
        calc1.num2 = 5;
        
        // Call instance method
        System.out.println("Sum: " + calc1.add());
        
        // Call method with parameters
        System.out.println("Product: " + calc1.multiply(3, 4));
        
        // Pass object to method
        Calculator calc2 = new Calculator();
        calc2.copyFrom(calc1);
        System.out.println("\nCalc2 after copying from Calc1:");
        calc2.display();
        
        // Return object from method
        Calculator calc3 = calc1.createCopy();
        System.out.println("\nCalc3 (copy of Calc1):");
        calc3.display();
    }
}

Output

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Previous Constructors

Next Access Modifiers →

Defining Methods

Calling Methods

Full Example

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