Set set

Catalog

One 、 characteristic

Two 、 Traverse

3、 ... and 、 Capacity expansion

Four 、 Realization

HashSet

TreeSet

Custom comparator

Pass the comparer through the constructor

  Implement sorting interface

---

One 、 characteristic

characteristic ： disorder , No repetition

How to go heavy

The list Construct a HashSet, Re pass HashSet Construct a ArrayList

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

The renderings are as follows ：

Two 、 Traverse

foreach, iterator

	private Set<Integer>set=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);
		
	}
	

    /**
	 * foreach Traverse 
	 */
	@Test
	public void test02() {
		for (Integer e : set) {
			System.out.println(e);
		}
	}
	
	/**
	 *  iterator 
	 */
	@Test
	public void test03() {
		Iterator<Integer> it = set.iterator();
		while(it.hasNext()) {
			System.out.println(it.next());
		}
	}
	

The renderings are as follows ：

3、 ... and 、 Capacity expansion

Capacity expansion ： Initial capacity 16, Load factor 0.75, Expansion increment 1 times

Four 、 Realization

• HashSet

It stores unique elements and allows null values , According to the hashcode To determine whether the element exists

Example ：

So let's set up a Student The entity class

package com.zking.set;

public class Student {

	private Integer sid;
	private String sname;
	private Integer sage;
	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 Integer getSage() {
		return sage;
	}
	public void setSage(Integer sage) {
		this.sage = sage;
	}
	public Student(Integer sid, String sname, Integer sage) {
		super();
		this.sid = sid;
		this.sname = sname;
		this.sage = sage;
	}
	public Student() {
		super();
	}
	@Override
	public String toString() {
		return "Student [sid=" + sid + ", sname=" + sname + ", sage=" + sage + "]";
	}

}

The test method

public void test04() {
		Set<Student>stu=new HashSet<>();
		stu.add(new Student(1," Eucalyptus Coicis ",18));
		stu.add(new Student(1," Eucalyptus Coicis ",18));
		stu.add(new Student(2," Thousand sails ",19));
		stu.add(new Student(3," mouse ",17));
		stu.add(new Student(4," The headset ",22));
		stu.add(new Student(5," An Nan ",30));
		
		for (Student s : stu) {
			System.out.println(s);
		}
	}

Running results ： Found no weight loss

  Override in entity class hascode as well as equals After the method

@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + ((sage == null) ? 0 : sage.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) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		Student other = (Student) obj;
		if (sage == null) {
			if (other.sage != null)
				return false;
		} else if (!sage.equals(other.sage))
			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;
	}

The renderings are as follows ： Go back to success  

Be careful ：HashSet The insertion order is not maintained , Non-thread safety

performance parameter ： Initial capacity , Load factor

1. The default value is ： Initial capacity 16, Load factor 0.75
2. Example ：new HashSet<>(20, 0.5f);

set Delete （ Remove elements ）

public void test05() {
		set.remove(7);
		System.out.println(set);
	}

The renderings are as follows ： 

• TreeSet

  Is a collection containing ordered elements without repetition , The function is to provide orderly Set aggregate , Sort naturally or according to what is provided Comparator Sort .TreeSet Is based on TreeMap Realized .

Example ： How to sort by age （ From big to small ）

	public void test04() {
     // Custom comparator 
		TreeSet<Student>stu=new TreeSet<>(new Comparator<Student>() {

			@Override
			public int compare(Student o1, Student o2) {
				
				return o2.getSage()-o1.getSage();
			}

			
		});
		stu.add(new Student(1," Eucalyptus Coicis ",18));
		stu.add(new Student(1," Eucalyptus Coicis ",18));
		stu.add(new Student(2," Thousand sails ",19));
		stu.add(new Student(3," mouse ",17));
		stu.add(new Student(4," The headset ",22));
		stu.add(new Student(5," An Nan ",30));
		
		for (Student s : stu) {
			System.out.println(s);
		}
	}

The renderings are as follows ：

Delete object

Custom comparator

• Pass the comparer through the constructor

public void test04() {
		TreeSet<Student>stu=new TreeSet<>(new Comparator<Student>() {

			@Override
			public int compare(Student o1, Student o2) {
				
				return o2.getSid()-o1.getSid();
			}

			
		});
		stu.add(new Student(1," Eucalyptus Coicis ",18));
		stu.add(new Student(1," Eucalyptus Coicis ",18));
		stu.add(new Student(2," Thousand sails ",19));
		stu.add(new Student(3," mouse ",17));
		stu.add(new Student(7," mouse ",18));
		stu.add(new Student(4," The headset ",22));
		stu.add(new Student(5," An Nan ",30));
		
		
		stu.remove(new Student(3," mouse ",17));
		for (Student s : stu) {
			System.out.println(s);
		}
	}

The renderings are as follows ： 

•   Implement sorting interface

package com.zking.set;

public class Student implements Comparable<Student>{

	private Integer sid;
	private String sname;
	private Integer sage;
	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 Integer getSage() {
		return sage;
	}
	public void setSage(Integer sage) {
		this.sage = sage;
	}
	public Student(Integer sid, String sname, Integer sage) {
		super();
		this.sid = sid;
		this.sname = sname;
		this.sage = sage;
	}
	public Student() {
		super();
	}
	@Override
	public String toString() {
		return "Student [sid=" + sid + ", sname=" + sname + ", sage=" + sage + "]";
	}
	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + ((sage == null) ? 0 : sage.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) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		Student other = (Student) obj;
		if (sage == null) {
			if (other.sage != null)
				return false;
		} else if (!sage.equals(other.sage))
			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;
	}
	@Override
	public int compareTo(Student o) {
		// TODO Auto-generated method stub
		return this.getSid()-o.getSid();
	}

}

Be careful ： When using the comparator to delete, pay attention to the fields in the comparator   If there are duplicate elements in the deleted data   If this element is the same as the field of the comparator Then a deletion error may occur . Because the comparator will sort according to the fields you set , If there is a repetition, it will be automatically de duplicated .

public void test04() {
		TreeSet<Student>stu=new TreeSet<>(new Comparator<Student>() {

			@Override
			public int compare(Student o1, Student o2) {
				
				return o2.getSage()-o1.getSage();
			}

			
		});
		stu.add(new Student(1," Eucalyptus Coicis ",18));
		stu.add(new Student(1," Eucalyptus Coicis ",18));
		stu.add(new Student(2," Thousand sails ",19));
		stu.add(new Student(3," mouse ",17));
		stu.add(new Student(7," mouse ",18));
		stu.add(new Student(4," The headset ",22));
		stu.add(new Student(5," An Nan ",30));
		
		
		stu.remove(new Student(3," mouse ",17));
		for (Student s : stu) {
			System.out.println(s);
		}
	}

The effect picture goes down ： You will find that you want to delete  Student(3," mouse ",17), But the Student(7," mouse ",18) Also deleted

  The solution is as follows ：

public void test04() { 
		TreeSet<Student>stu=new TreeSet<>(new Comparator<Student>() {

			@Override
			public int compare(Student o1, Student o2) {
				if(o1.getSage()-o2.getSage()==0) {
					return o1.getSid()-o2.getSid();
				}
				return o1.getSage()-o2.getSage();
			
			}

			
		});
		//stu.add(new Student(1," Eucalyptus Coicis ",18));
		stu.add(new Student(1," Eucalyptus Coicis ",18));
		stu.add(new Student(2," Thousand sails ",19));
		stu.add(new Student(3," mouse ",17));
		stu.add(new Student(7," mouse ",18));
		stu.add(new Student(4," The headset ",22));
		stu.add(new Student(5," An Nan ",30));
		
		
		stu.remove(new Student(3," mouse ",17));
		for (Student s : stu) {
			System.out.println(s);
		}
	}

The renderings are as follows ：