集合框架-ArrayList练习(去除ArrayList集合中的重复元素)

package cn.itcast.p3.arraylist.test;

import java.util.ArrayList;
import java.util.Iterator;

import com.sun.org.apache.bcel.internal.generic.NEW;

import cn.itcast.p.bean.Person;
import cn.itcast.p4.hashset.demo.HashSetDemo;

/*
 * 定义功能去除ArrayList中的重复元素
 */
public class ArrayListTest2 {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        
        ArrayList al = new ArrayList();
        al.add(new Person("list1",21));
        al.add(new Person("list2",22));
        al.add(new Person("list3",23));
        al.add(new Person("list4",24));
        al.add(new Person("list4",24));
        al.add(new Person("list4",24));
        
        System.out.println(al);
        
        al = getSingleElement(al);
        
        System.out.println(al);
        
//        System.out.println(al.remove(new Person("list2",22)));//remove 也是和equals相关
        
//        System.out.println(al);
        
//        singleDemo();
    }
    
    private static ArrayList getSingleElement_2(ArrayList al) {
        // TODO Auto-generated method stub
        return null;
    }

    /**
     * 
     */
    public static void singleDemo() {
        ArrayList al = new ArrayList();
        al.add("abc1");
        al.add("abc2");
        al.add("abc2");
        al.add("abc1");
        al.add("abc");
        System.out.println(al);
        al = getSingleElement(al);
        System.out.println(al);
        
        
    }
    public static ArrayList getSingleElement(ArrayList al) {
        //1，定义一个临时容器
        ArrayList temp = new ArrayList();
        
        //2,迭代al集合
        Iterator it = al.iterator();
        
        while(it.hasNext()) {
            Object obj = it.next();
            //3,判断被迭代到的元素是否在临时容器存在。
            if (!temp.contains(obj)) {//contains也是依据equals，如果person类equals没有重写，比较的还是地址值
                temp.add(obj);
            }
        }
        
        return temp;
    }

    

}

package cn.itcast.p.bean;

public class Person {
    private String name;
    private int age;
    
    
    public Person() {
        super();
        // TODO Auto-generated constructor stub
    }
    public Person(String name, int age) {
        super();
        this.name = name;
        this.age = age;
    }
    
    @Override
    public int hashCode() {
        System.out.println(this+".....hashCode");
        // TODO Auto-generated method stub
        return name.hashCode()+age*27;//age后面乘以一个数增大离散程度，减少返回哈希值相等的几率
                                    //好比张三哈希值20 年龄40  李四哈希值30，年龄30 结果哈希值一样
                                    //乘一个数后就不一样了离散程度变大了
        
        
        //return 100;//会比较equals
    }
    public boolean equals(Object obj) {
        //健壮性
        if (this == obj) {//有可能传入相同的对象，可以先行判断是否为同一对象add(p) add(p)这种传入两次
            return true;
        }
        if (!(obj instanceof Person)) {//判断是否为Person类型，类型不一致也不应该传入
            throw new ClassCastException("类型错误");
        }
        
//        System.out.println(this+"...equals...."+obj);
        Person p = (Person)obj;
        
        
        return this.name.equals(p.name) && this.age == p.age;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    //ctrl+alt+s 快捷构造set，get方法 初始化等
    public String toString() {
        return name+":"+age;
    }
}