1. Set目录

 1.1 特点：无序、对象不能重复

 

1.2 遍历
    1.2.1 foreach
    1.2.2 迭代器    

 

	
	Set set =new HashSet<>();
	set.add(new Student(1,"zs",100f));
	set.add(new Student(2,"ls",20f));
	set.add(new Student(3,"ww",30f));
	set.add(new Student(4,"zs",100f));
	//1）默認 使用equals比較，objcet类型是引用类型，默认比较的是内存地址
	//2）重寫hashCode和equals類型是引用類型，先比較hashCode的值是否相同，在比較equels
	//hascode值相同，则比较equals
	//hascode值不相同，则不比较equals
//	Student stu=new Student();
//	stu.equals(null);
	//set.forEach(System.out::println);

	//遍历方式（2种）
	//1)foreach
	for (Student student : set) {
		
		System.out.println(student);
	}
	System.out.println("----------------");
	//2)iterator迭代器
	//获取遍历
	Iterator it=set.iterator();
	//遍历循环
	while(it.hasNext()) {
		System.out.println(it.next());
	}

 1.3 常用实现类
      HashSet
      TreeSet：根据某种(规则)对里面的元素进行排序
        自然比较接口: java.lang.Comparable 
        比较器: java.util.Comparator
        String以AscII码进行比较，返回差值

Student实体类 

public class Student implements Serializable, Comparable {
	private int sid;
	private String sname;
	private Float score;

	public Student(int sid, String sname, Float score) {
		super();
		this.sid = sid;
		this.sname = sname;
		this.score = score;
	}

	public Student() {
		super();
	}

	public int getSid() {
		return sid;
	}

	public void setSid(int sid) {
		this.sid = sid;
	}

	public String getSname() {
		return sname;
	}

	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + ((score == null) ? 0 : score.hashCode());
		result = prime * result + sid;
		result = prime * result + ((sname == null) ? 0 : sname.hashCode());
		return result;
	}

	@Override
	public boolean equals(Object obj) {
		
		if (this == obj)
			return true;
		// obj是否为空
		if (obj == null)
			return false;
		// 当前对象类型与obj类型不相同
		if (getClass() != obj.getClass())
			return false;
		Student other = (Student) obj;
		if (this.getSid() == other.getSid())
			return false;
		return true;
	}

	public void setSname(String sname) {
		this.sname = sname;
	}

	public Float getScore() {
		return score;
	}

	public void setScore(Float score) {
		this.score = score;
	}

	@Override
	public String toString() {
		return "Student [sid=" + sid + ", sname=" + sname + ", score=" + score + "]";
	}

	@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
		
		//降序)
		// return -(this.getSid()-o.getSid());
		//(升序和
		 //return this.getSid()-o.getSid();
		return this.getSname().hashCode()-o.getSname().hashCode();
	}

 Demo1

public static void main(String[] args) {
//TreeSet:以某种特定的的规则对集合中的元素进行排序(升序和降序)
	//java.lang.Comparable:自然比较接口必须在类里面实现接口 然后重新方法
	java.util.Comparable:比较器（推荐）
	//字母进行了排序（升序）
	Set set1 =new TreeSet<>();
	set1.add("zs");
	set1.add("ls");
	set1.add("ww");
	
	//类错误
	Set set =new TreeSet<>(new NameComparator());
	set.add(new Student(1,"zs",100f));
	set.add(new Student(2,"ls",20f));
	set.add(new Student(3,"ww",30f));
	
	set.forEach(System.out::println);
}

NameComparator类 

public class NameComparator implements Comparator{

	 //比较器: java.util.Comparator
	//Student o1与 Student o2作比较
	public int compare(Student o1, Student o2) {

		return o1.getSid()-o2.getSid();
	}
//      String以AscII码进行比较，返回差值