HashSet和TreeSet

package com.wzy.list;

import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
import java.util.TreeSet;

class Student1 implements Comparable{
    private Integer id;
    private String name;

    public Student1(String name,Integer id) {
        this.id = id;
        this.name = name;
    }
    @Override
    public String toString() {
        return "name:"+name+"; id:"+id;
    }
    @Override
    public int compareTo(Object o) {
        if(this.id > ((Student1)o).id) {
            return ;
        }else if(this.id < ((Student1)o).id) {
            return -;
        }else{
            return this.name.compareTo(((Student1)o).name);
        }

    }
}

class Student2{
    private Integer id;
    private String name;

    public Student2(String name,Integer id) {
        this.id = id;
        this.name = name;
    }

    @Override
    public int hashCode() {
        final int prime = ;
        int result = ;
        result = prime * result + ((id == null) ?  : id.hashCode());
        result = prime * result + ((name == null) ?  : name.hashCode());
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Student2 other = (Student2) obj;
        if (id == null) {
            if (other.id != null)
                return false;
        } else if (!id.equals(other.id))
            return false;
        if (name == null) {
            if (other.name != null)
                return false;
        } else if (!name.equals(other.name))
            return false;
        return true;
    }

    @Override
    public String toString() {
        return "Student2 [id=" + id + ", name=" + name + "]";
    }    

}
public class Test02 {
    public static void main(String[] args) {
        /**
         * TreeSet和HashSet存入对象时，不会自动去重操作
         *
         * TreeSet去掉重复对象，基于Comparable接口实现
         * HashSet去掉重复对象，基于equals和hashCode实现
         * TreeSet可以对象排序，hashSet不可以
         *
         * 如果存入的不是new出来的对象，
         * 而是String或int类型，可以直接使用，不必实现上述操作
         * **/

        //TreeSet存入对象实例
        Set<Student1> stu1 = new TreeSet<Student1>();
        stu1.add(new Student1("aa",));
        stu1.add(new Student1("bb",));//id重复
        stu1.add(new Student1("dd",));
        stu1.add(new Student1("cc",));
        stu1.add(new Student1("aa",));//对象重复
        Iterator s = stu1.iterator();
        while(s.hasNext()) {
            System.out.println(s.next());
        }

        //HashSet存入对象实例
        Set<Student2> stu2 = new HashSet<Student2>();
        stu2.add(new Student2("aa",));
        stu2.add(new Student2("bb",));
        stu2.add(new Student2("cc",));
        stu2.add(new Student2("dd",));
        stu2.add(new Student2("ee",));
        stu2.add(new Student2("aa",));

        Iterator i = stu2.iterator();
        while(i.hasNext()) {
            System.out.println(i.next());
        }

        //TreeSet存入普通字符串
        Set set1 = new TreeSet();
        set1.add("a");
        set1.add("aa");
        set1.add("d");
        set1.add("b");
        set1.add("c");
        //[a, aa, b, c, d] TreeSet已经自动排序好了
        System.out.println(set1);

        //HashSet存入普通字符串
        Set set2 = new HashSet();
        set2.add("a");
        set2.add("aa");
        set2.add("d");
        set2.add("c");
        set2.add("b");
        //[aa, a, b, c, d] HashSet不会排序
        System.out.println(set2);
    }
}