Java 變數指定

import java.util.ArrayList;

public class VariableAssignDemo {

 public static void main(String[] args){
  ArrayList a1 = new ArrayList();
  a1.add(1);
  /**
   * Following case assigns object reference to a new variable
   */
  ArrayList a2 =a1;
  a2.add(2);
  System.out.println(a1.toString());
  System.out.println(a2.toString());
  
  System.out.println("-------------------");
  
  /**
   * Following is a deep copy , all elements are included..
   * If you want to keep original object , but do some changes on it.
   * A deep copy is a solution.
   */
  ArrayList a4 =new ArrayList();
  for(int i = 0 ;i < a1.size() ;i++){
   a4.add(a1.get(i));
  }
  a1.remove(0);
  System.out.println(a1.toString());
  System.out.println(a4.toString());
  
 }
}