Java: Adding fields and methods to existing Class?

Question

Is there, in Java, a way to add some fields and methods to an existing class? What I want is that I have a class imported to my code, and I need to add some fields, derived from the existing fields, and their returning methods. Is there any way to do this?

Answer 1

You can create a class that extends the one you wish to add functionality to:

public class sub extends Original{  ... } 

To access any of the private variables in the superclass, if there aren't getter methods, you can change them from "private" to "protected" and be able to reference them normally.

Hope that helps!

Answer 2

You can extend classes in Java. For Example:

public class A {    private String name;    public A(String name){     this.name = name;   }    public String getName(){     return this.name;   }    public void setName(String name) {     this.name = name;   }  }  public class B extends A {   private String title;    public B(String name, String title){     super(name); //calls the constructor in the parent class to initialize the name     this.title= title;   }          public String getTitle(){     return this.title;   }    public void setTitle(String title) {     this.title= title;   } } 

Now instances of B can access the public fields in A:

B b = new B("Test"); String name = b.getName(); String title = b.getTitle(); 

For more detailed tutorial take a look at Inheritance (The Java Tutorials > Learning the Java Language > Interfaces and Inheritance).

Edit: If class A has a constructor like:

public A (String name, String name2){   this.name = name;   this.name2 = name2; } 

then in class B you have:

public B(String name, String name2, String title){   super(name, name2); //calls the constructor in the A    this.title= title; }