1 Set接口概述
- 一个不包含重复元素的Collection。
2 HashSet类
2.1 HashSet类的概述
- 它不保证Set的迭代顺序，特别是它不保证该顺序恒久不变。
- 底层数据结构是哈希表。
- 添加功能依赖于两个方法：
public int hashCode()
public boolean equals(Object obj)
2.2 HashSet的应用
- 应用：
package com.xuweiwei;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
/**
* @author 许威威
* @version 1.0
*/
public class SetDemo {
public static void main(String[] args) {
Set<String> set = new HashSet<>();
set.add("hello");
set.add("world");
for(Iterator<String> iterator = set.iterator();iterator.hasNext();){
String str = iterator.next();
System.out.println("str = " + str);
}
System.out.println("------------------------");
for (String s : set) {
System.out.println("s = " + s);
}
}
}
- 示例：
package com.xuweiwei;
import java.util.Objects;
/**
* @author 许威威
* @version 1.0
*/
public class Student {
private String name;
private Integer age;
public Student() {
}
public Student(String name, Integer age) {
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
Student student = (Student) o;
return Objects.equals(name, student.name) &&
Objects.equals(age, student.age);
}
@Override
public int hashCode() {
return Objects.hash(name, age);
}
@Override
public String toString() {
return "Student{" +
"name=‘" + name + ‘\‘‘ +
", age=" + age +
‘}‘;
}
}
package com.xuweiwei;
import java.util.HashSet;
import java.util.Set;
/**
* @author 许威威
* @version 1.0
*/
public class SetDemo2 {
public static void main(String[] args) {
Set<Student> set = new HashSet<>();
set.add(new Student("张三",20));
set.add(new Student("李四",20));
set.add(new Student("张三",20));
set.add(new Student("李四",30));
set.add(new Student("王五",20));
set.add(new Student("王五",35));
set.add(new Student("王五",25));
for (Student student : set) {
System.out.println("student = " + student);
}
}
}
3 LinkedHashSet类
3.1 LinkedHashSet类概述
- 元素有序且唯一。
- 由链表保证元素有序。
- 由哈希表保证元素唯一。
3.2 LinkedHashSet的应用
- 示例：
package com.xuweiwei;
import java.util.LinkedHashSet;
import java.util.Set;
/**
* @author 许威威
* @version 1.0
*/
public class LinkedHashSetDemo {
public static void main(String[] args) {
Set<String> set = new LinkedHashSet<>();
set.add("hello");
set.add("world");
set.add("java");
set.add("hello");
for (String s : set) {
System.out.println("s = " + s);
}
}
}
4 TreeSet类
4.1 TreeSet类概述
- 使用元素的自然顺序对元素进行排序（自然排序）。
- 可以根据创建set时候提供的Comparator进行排序（比较器排序）。
- 具体取决于使用的构造方法。
4.2 TreeSet是如何保证元素的排序和唯一性的
- 底层数据结构是红黑树。
4.3 TreeSet的应用
- 示例：自然排序
package com.xuweiwei;
import java.util.Set;
import java.util.TreeSet;
/**
* @author 许威威
* @version 1.0
*/
public class TreeSetDemo {
public static void main(String[] args) {
Set<Integer> set = new TreeSet<>();
set.add(20);
set.add(18);
set.add(23);
set.add(22);
set.add(17);
set.add(24);
set.add(19);
set.add(18);
set.add(24);
for (Integer i : set) {
System.out.println("i = " + i);
}
}
}
- 示例：TreeSet存储自定义对象并保证排序和唯一（自然排序）
package com.xuweiwei;
/**
* @author 许威威
* @version 1.0
*/
public class Student implements Comparable<Student> {
private String name;
private Integer age;
public Student() {
}
public Student(String name, Integer age) {
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
@Override
public int compareTo(Student o) {
int num = this.getAge() - o.getAge();
return num == 0 ? this.getName().compareTo(o.getName()) : num;
}
@Override
public String toString() {
return "Student{" +
"name=‘" + name + ‘\‘‘ +
", age=" + age +
‘}‘;
}
}
package com.xuweiwei;
import java.util.Set;
import java.util.TreeSet;
/**
* @author 许威威
* @version 1.0
*/
public class TreeSetDemo {
public static void main(String[] args) {
Set<Student> set = new TreeSet<>();
set.add(new Student("张三",20));
set.add(new Student("张三",30));
set.add(new Student("李四",20));
set.add(new Student("王五",90));
set.add(new Student("赵六",7));
set.add(new Student("田七",10));
set.add(new Student("王八",35));
for (Student student : set) {
System.out.println("student = " + student);
}
}
}
- 示例：比较器排序
package com.xuweiwei;
/**
* @author 许威威
* @version 1.0
*/
public class Student {
private String name;
private Integer age;
public Student() {
}
public Student(String name, Integer age) {
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
@Override
public String toString() {
return "Student{" +
"name=‘" + name + ‘\‘‘ +
", age=" + age +
‘}‘;
}
}
package com.xuweiwei;
import java.util.Comparator;
import java.util.Set;
import java.util.TreeSet;
/**
* @author 许威威
* @version 1.0
*/
public class TreeSetDemo {
public static void main(String[] args) {
Set<Student> set = new TreeSet<>(new Comparator<Student>() {
@Override
public int compare(Student o1, Student o2) {
int num = o1.getAge() - o2.getAge();
return num == 0 ? o1.getName().compareTo(o2.getName()) : num;
}
});
set.add(new Student("张三", 20));
set.add(new Student("张三", 30));
set.add(new Student("李四", 20));
set.add(new Student("王五", 90));
set.add(new Student("赵六", 7));
set.add(new Student("田七", 10));
set.add(new Student("王八", 35));
for (Student student : set) {
System.out.println("student = " + student);
}
}
}
原文地址：https://www.cnblogs.com/xuweiweiwoaini/p/9350923.html
时间： 2024-08-28 16:53:23