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

Answer 1

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;
}