how to call another class method in java

Daniel Parker

2 min read

·

07-02-2025

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Calling methods from other classes in Java is a fundamental aspect of object-oriented programming. It allows for code reusability and promotes a modular design. This article will guide you through various techniques to achieve this, catering to different scenarios and complexities. We'll cover calling methods within the same class, calling methods from different classes within the same package, and calling methods from classes in different packages.

Calling Methods Within the Same Class

This is the simplest scenario. You can directly call a method from another method within the same class using its name.

public class MyClass {

    private int x;

    public void setX(int value) {
        x = value;
    }

    public int getX() {
        return x;
    }

    public void printX(){
        int val = getX(); //Calling getX() method within the same class
        System.out.println("Value of x: " + val);
    }

    public static void main(String[] args) {
        MyClass obj = new MyClass();
        obj.setX(10);
        obj.printX(); // Calling printX() method which in turn calls getX()
    }
}

In this example, printX() directly calls getX() to retrieve and display the value of x.

Calling Methods from Different Classes in the Same Package

When calling methods from different classes within the same package, you need to create an instance (object) of the class containing the method you want to call.

package mypackage;

class ClassA {
    public void methodA() {
        System.out.println("Method A from ClassA");
    }
}

public class ClassB {
    public static void main(String[] args) {
        ClassA objA = new ClassA(); //Creating an instance of ClassA
        objA.methodA(); //Calling methodA() from ClassA
    }
}

Here, ClassB creates an object objA of ClassA and then uses this object to call methodA().

Calling Methods from Classes in Different Packages

Calling methods across packages requires understanding access modifiers (public, private, protected, default). Only public methods can be accessed directly from other packages.

Example:

Let's say ClassA is in package package1 and ClassB is in package package2.

package1/ClassA.java:

package package1;

public class ClassA {
    public void publicMethod() {
        System.out.println("Public method called");
    }

    private void privateMethod() {
        System.out.println("Private method - cannot be accessed from outside the class");
    }
}

package2/ClassB.java:

package package2;

import package1.ClassA; //Import the ClassA class

public class ClassB {
    public static void main(String[] args) {
        ClassA objA = new ClassA();
        objA.publicMethod(); //Calling the public method
        //objA.privateMethod();  //This would cause a compile-time error
    }
}

ClassB can only access the publicMethod() of ClassA. Attempts to call privateMethod() will result in a compilation error.

Static Methods

Calling static methods is slightly different. You don't need to create an object; you call them directly using the class name.

package mypackage;

class ClassA {
    public static void staticMethod() {
        System.out.println("Static method called");
    }
}

public class ClassB {
    public static void main(String[] args) {
        ClassA.staticMethod(); //Calling static method directly using class name
    }
}

Best Practices

• Encapsulation: Use appropriate access modifiers (public, private, protected) to control access to methods. Favor private methods for internal use and public methods for external interaction.
• Modularity: Break down your code into smaller, manageable classes with well-defined responsibilities.
• Clear Naming Conventions: Use descriptive names for your classes and methods to improve code readability.
• Error Handling: Incorporate error handling (e.g., try-catch blocks) to gracefully manage potential exceptions.

By following these guidelines, you can effectively call methods from other classes in Java, building robust and maintainable applications. Remember to consider access modifiers and whether the method is static or not when making your calls.