_ArrayList_HashSet的比较

public class ReflectPoint {
 private int x;
 public int y;
 public String str1="ball";
 public String str2="basketball";
 public String str3="itcast";
 public ReflectPoint(int x, int y) {
  super();
  this.x = x;
  this.y = y;
 }
 
 
/* @Override
 public int hashCode() {
  final int prime = 31;
  int result = 1;
  result = prime * result + x;
  result = prime * result + y;
  return result;
 }

 @Override
 public boolean equals(Object obj) {
  if (this == obj)
   return true;
  if (obj == null)
   return false;
  if (getClass() != obj.getClass())
   return false;
  ReflectPoint other = (ReflectPoint) obj;
  if (x != other.x)
   return false;
  if (y != other.y)
   return false;
  return true;
 }
*/
 /*当添加上面这段代码后，pt1与pt3相等，当使用HashSet时，就只放入了两个
  * 元素*/

 public String toString(){
  return str1+" "+str2+" "+str3;
  
 }
}

 

 

import java.lang.reflect.Array;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.HashSet;

public class ReflectTest {
 public static void main(String[] args) throws Exception {

  Collection collections = new HashSet();
  //Collection collections = new ArrayList();
  /*ArrayList是一种有顺序的集合，把对象的引用放入一个相当于数组的容器
   * 当有相同的对象放进去时，只是不同位置放入的引用变量相同，此时可以放进去
   * 而HashSet先判断两个对象是否相等，如果相等则不放入，所以当collections
   * 为HashSet时，collections长度为3，而用ArrayList时collections长度为4*/
  ReflectPoint pt1 = new ReflectPoint(3,3);
  ReflectPoint pt2 = new ReflectPoint(5,5);
  ReflectPoint pt3 = new ReflectPoint(3,3); 

  collections.add(pt1);
  collections.add(pt2);
  collections.add(pt3);
  collections.add(pt1); 
  
  
  
  System.out.println(collections.size());
 }

 
 }