集合框架【第二章】——Set（HashSet与TreeSet）

public class Student implements Serializable,Comparable<Student>{

	/**
	 * 
	 */
	private static final long serialVersionUID = 1L;
	private Integer sid;
	private String sname;
	private Float score;
	public Integer getSid() {
		return sid;
	}
	public void setSid(Integer sid) {
		this.sid = sid;
	}
	public String getSname() {
		return sname;
	}
	public void setSname(String sname) {
		this.sname = sname;
	}
	public Float getScore() {
		return score;
	}
	public void setScore(Float score) {
		this.score = score;
	}
	
	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + ((score == null) ? 0 : score.hashCode());
		result = prime * result + ((sid == null) ? 0 : sid.hashCode());
		result = prime * result + ((sname == null) ? 0 : sname.hashCode());
		return result;
	}
	@Override
	public boolean equals(Object obj) {
		//true代表已存在，false代表允许添加（不存在）
		//当前对象是否与obj对象相同
		if (this == obj)
			return true;
		//obj对象是否为空
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		//当前对象类型与obj对象类型不相同
		Student other = (Student) obj;
		if(this.getSid()==other.getSid()) {
			return true;
		}
		return true;
	}
	public Student(Integer sid, String sname, Float score) {
		super();
		this.sid = sid;
		this.sname = sname;
		this.score = score;
	}
	public Student() {
		super();
	}
	@Override
	public String toString() {
		return "Student [sid=" + sid + ", sname=" + sname + ", score=" + score + "]";
	}
	/*@Override
	public int compareTo(Student o) {
		return -(this.getSid()-o.getSid());
	}*/
	@Override
	public int compareTo(Student o) {
		//比较者大于被比较者返回1
		//比较者等于被比较者返回0
		//比较者小于被比较者返回-1
		/*if(this.getSid()>o.getSid()) 
			return 1;
		else {
			if(this.getSid()==o.getSid()) 
				return 0;
			else 
				return -1;
			}*/
		
		//return this.getSid()-o.getSid();
		return this.getSname().hashCode()-o.getSname().hashCode();
		}	

package com.zking.Collection.util;

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

import com.zking.Collection.entity.Student;

public class Demo1 {

	public static void main(String[] args) {
		//Set
		//1.特点：无序，唯一
		//1)无序：元素添加的顺序与输出的不一致
		//2)唯一：不允许添加重复元素(被过滤掉了)
		//问题：元素是被覆盖还是过滤
		/*Set<String> set=new HashSet<>();
		set.add("a");
		set.add("b");
		set.add("c");
		set.add("d");
		
		set.forEach(System.out::println);*/
		
		Set<Student> set=new HashSet<>();
		set.add(new Student(1, "a", 100f));
		set.add(new Student(2, "b", 70f));
		set.add(new Student(3, "c", 80f));
		set.add(new Student(1, "a", 90f));
		
		//1)默认使用equals比较，Object类型是引用类型，默认比较的是内存地址
		//2)重新hashcode和equals方法，先比较hashcode值是否相同，再比较equals
		//2.1)hashcode值相同，则比较equals
		//2.2)hashcode值不相同，则不比较equals
		/*Student stu=new Student();
		stu.equals(null);*/
		//set.forEach(System.out::println);
		//2.遍历方式（2种）
		//1）foreach
		for(Student student: set) {
			System.out.println(student);
		}
		System.out.println("-------------");
		//2)iterator(迭代器)
		//获取迭代器
		Iterator<Student> it= set.iterator();
		//循环遍历
		while(it.hasNext()) {
			System.out.println(it.next());
		}
	}
}

public static void main(String[] args) {
		//TreeSet:以某种特定的规则对集合中的某种元素进行排序（升序和降序）
		//java.lang.Comparable:自然比较接口
		//java.util.Comparator:比较器（推荐）
		
		/*Set<String> set=new TreeSet<>();
		set.add("hh");
		set.add("mm");
		set.add("zz");
		set.add("dd");*/
		
		Set<Student> set=new TreeSet<>(new NameComparator());
		set.add(new Student(1, "hh", 100f));
		set.add(new Student(2, "mm", 70f));
		set.add(new Student(3, "zz", 80f));
		set.add(new Student(1, "dd", 90f));
		set.forEach(System.out::println);
		
	}

package com.zking.Collection.util;

import java.util.Comparator;

import com.zking.Collection.entity.Student;

public class NameComparator implements Comparator<Student> {


	@Override
	public int compare(Student o1, Student o2) {
		// TODO Auto-generated method stub
		return o1.getSid()-o2.getSid();
	}

}