如何更改Java类的predifine方法

Question

I want to change in predefined method of ArrayList class. suppose if we add any element to arraylist . simultaneously system will print "value is added in arraylist" . is it possible to do changes on add() of ArrayList class.

Answer 1

In this situation composition is usually preferred over inheritance (see http://en.wikipedia.org/wiki/Composition_over_inheritance ).

For example, if you follow the approach of extending the ArrayList class, do you also want your logic invoked when add(int index, E element) is called. What about addAll(Collection<? extends E> c) . What if a new add method is added in a subsequent version of Java?

Instead, consider implementing your own List . Internally it would delegated operations to an ArrayList , but you are forced to think about how to handle each type of addition.

Answer 2

public class foo extends ArrayList<Object> {
  @Override
  public boolean add(Object e) {
    // print your stuff here
    return super.add(e);
  }
}

Answer 3

Are you asking about method overriding ??

public class MyArrayLIst  extends ArrayList<ClassObj>{

   @Override
   public void add(ClassObj obj) {
      //sysout
      return super.add(obj);

   }


}

Answer 4

make your own overridden add method which calls add method of ArrayList and prints what you want as well. must be done with inheriting the class.