Collection collection system

Collection collection system introduced

Collection set of map:

　　

List collection:

　　　Ordered set, reference ArrayList and LinkedList comparison article,

Set Collection:

　　　Unordered set, there is no concept of index, index access does not pass.

HashSet：

　　HashSet the elements can not be repeated, is determined based on the first comparison target hashCode values ​​are equal if they are equal then the comparison target address.

Equals and hashCode method can override comparison rules redefine classes:

	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + age;
		result = prime * result + ((name == null) ? 0 : name.hashCode());
		return result;
	}
	
	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 (name == null) {
			if (other.name != null)
				return false;
		} else if (!name.equals(other.name))
			return false;
		return true;
	}
}

TreeSet

　　Features: You can sort the natural elements of the collection, if you want to specify a collation, the Comparable interface can be inherited, or create a TreeSet time, specify a class object Comparable interface

 1 package set;
 2 
 3 import java.util.Comparator;
 4 import java.util.Set;
 5 import java.util.TreeSet;
 6 
 7 public class TestTreeSet {
 8     public static void main(String[] args) {
28         Set<Person> pSet2 = new TreeSet<Person>(new Comparator<Person>() {
29             public int compare(Person o2, Person o1) {
30                 int result = (o1.name+"").compareTo(o2.name+"");
31                 IF (Result == 0) { // represents two strings are equal 
32                      return o2.age - o1.age;
 33 is                  }
 34 is                  return Result;
 35              }
 36          });
 37 [          pSet2.add ( new new the Person ( "John Doe" , 20 is)); // zhangsan 
38 is          pSet2.add ( new new the Person ( "John Doe", 30)); // Lisi 
39          pSet2.add ( new new the Person ( "John Doe", 25)); // Lisi 
40          pset2 .add ( new new the Person ( "Cong", 30)); // licong
41         pSet2.add(new Person("周瑞发", 30)); // zhourunfa
42         for (Person person : pSet2) {
43             System.out.println(person);
44         }
45     }
46 }
47 
48 class Person /*implements Comparable<Person>*/{
49     String name;
50     int age;
51     
52     public Person(String name, int age) {
53         super();
54         this= .name name;
 55          the this .age = Age;
 56 is      }
 57 is      
58      / * public int compareTo (the Person O) {
 59          // String object implements compareTo method, sorted according to the natural ordering rules
 60          int Result = (+ o.name "") .compareTo (this.name + "");
 61 is          IF (Result == 0) {// represents two strings are equal
 62 is              return this.age - o.age;
 63 is          }
 64          return Result;
 65      } * / 
66  
67      public String toString () {
 68          return "the Person [name =" + name + ", Age =" + Age + "]" ;
69     }
70 }

 

LinkedHashSet：

　　Features: orderly, unrepeatable container

　　

Map collection system:

　　

Unimportant, self-Baidu