java集合（set集合）

1. set集合中元素是无序的。

2. set集合中元素是不可重复的。

foreach，迭代器

• HashSet

1. 非线程安全
2. 由HashMap支持
3. 不保持插入顺序
4. 它存储唯一元素并允许空值 (依据对象的hashcode来确定该元素是否存在
5. 性能参数：初始容量，负载因子 (默认值： 初始容量16，负载因子0.75

1.如何去重

	
	private List list = new ArrayList<>();
	
    @BeforeAll
	public void setup() {
		set.add(1);
		set.add(1);
		set.add(2);
		set.add(2);
		set.add(3);
		set.add(3);
	}
	
	@Test
	public void test01() {
		List tmp = new ArrayList<>(new HashSet(list));
		System.out.println(tmp);
	}

1.  foreach遍历，迭代器

 
	private Setset=new HashSet<>();
	
	@Before
	public void setup() {
		set.add(1);
		set.add(2);
		set.add(2);
		set.add(3);
		set.add(4);
		set.add(5);
		set.add(6);
		set.add(7);
		
	}
	
 
    
	@Test
	public void test02() {
		for (Integer e : set) {
			System.out.println(e);
		}
	}
	
	
	@Test
	public void test03() {
		Iterator it = set.iterator();
		while(it.hasNext()) {
			System.out.println(it.next());
		}
	}

• TreeSet 

1. TreeSet是基于TreeMap实现的
2. 作用是提供有序的Set集合，自然排序或者根据提供的Comparator进行排序
3. 是一个包含有序的且没有重复元素的集合

创建一个实体类,实现排序接口

public class Student implements Comparable{
	
	private Integer sid;	
	private String sname;
	private int age;
 
	public Student(Integer sid, String sname, int age) {
		super();
		this.sid = sid;
		this.sname = sname;
		this.age = age;
	}
 
	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 int getAge() {
		return age;
	}
 
	public void setAge(int age) {
		this.age = age;
	}
 
}

 实现hashCode和equals方法：

    
    @Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + age;
		result = prime * result + ((sid == null) ? 0 : sid.hashCode());
		result = prime * result + ((sname == null) ? 0 : sname.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;
		Student other = (Student) obj;
		if (age != other.age)
			return false;
		if (sid == null) {
			if (other.sid != null)
				return false;
		} else if (!sid.equals(other.sid))
			return false;
		if (sname == null) {
			if (other.sname != null)
				return false;
		} else if (!sname.equals(other.sname))
			return false;
		return true;//学号名字年龄都相等才是同一个学生
	}
 
	@Override
	public String toString() {
		return "Student [s + sid + ", sname=" + sname + ", age=" + age + "]";
	}
    
    
	@Override
	public int compareTo(Student o) {
		if(this.getAge()-o.getAge()==0) {
			return this.getSid()-o.getSid();
		}
		return this.getAge() - o.getAge();
	}

 再使用ThreeSet

    @Test
	public void test04() {
		TreeSet stu = new TreeSet<>();
		
		stu.add(new Student(1,"zs", 18));
		stu.add(new Student(1,"zs", 18));
		stu.add(new Student(2,"ls", 19));
		stu.add(new Student(4,"lihao", 10));
		stu.add(new Student(7,"lihao", 18));
		stu.add(new Student(5,"zengfanyan", 20));
		stu.add(new Student(3,"we", 30));
				
		for(Student s: stu) {
			System.out.println(s);
		}
	}