JavaSE——集合框架一（5/7）-Set系列集合：Set集合的特点、底层原理、哈希表、去重复原理

import java.util.HashSet;
import java.util.LinkedHashSet;
import java.util.Set;
import java.util.TreeSet;
 
public class SetDemo1 {
    public static void main(String[] args){
        //1.创建一个Set集合的对象
//        Set<Integer> set = new HashSet<>();         //创建了一个HashSet的集合对象   经典代码  HashSet：无序不重复无索引
//        Set<Integer> set = new LinkedHashSet<>();   //有序 不重复 无索引
        Set<Integer> set = new TreeSet<>();
        set.add(666);
        set.add(555);
        set.add(555);
        set.add(888);
        set.add(888);
        set.add(777);
        set.add(777);
        System.out.println(set);
    }
}

public class SetDemo2 {
    public static void main(String[] args) {
        /*
        Java中的所有对象，都可以调用Object类提供的hashCode方法，返回该对象自己的哈希值
            public int hashCode():  返回对象的哈希值.
        同一个对象多次调用hashCode()方法返回的哈希值是相同的.
        不同的对象，它们的哈希值一般不相同，但也有可能会相同(哈希碰撞)
         */
        Student s1 = new Student("蜘蛛精",25,169.5);
        Student s2 = new Student("紫霞",22,166.5);
        System.out.println("第一次取s1的哈希值： " + s1.hashCode());
        System.out.println("第二次取s1的哈希值： " + s1.hashCode());
        System.out.println("第一次取s2的哈希值： " + s2.hashCode());
        System.out.println("第二次取s2的哈希值： " + s2.hashCode());
 
        System.out.println();
 
        //哈希碰撞
        String str1 = new String("abc");
        String str2 = new String("acD");
        System.out.println("str1的哈希值： " + str1.hashCode());
        System.out.println("str2的哈希值： " + str2.hashCode());
    }
}

import java.util.HashSet;
import java.util.Set;
 
public class SetDemo3 {
    public static void main(String[] args) {
        Set<Student> students = new HashSet<>();
        Student s1 = new Student("至尊宝",28,169.6);
        Student s2 = new Student("蜘蛛精",23,169.6);
        Student s3 = new Student("蜘蛛精",23,169.6);
        System.out.println("s2的哈希值： " + s2.hashCode());
        System.out.println("s3的哈希值： " + s3.hashCode());
        Student s4 = new Student("牛魔王",48,169.6);
        students.add(s1);
        students.add(s2);
        students.add(s3);
        students.add(s4);
        System.out.println(students);
    }
}

import java.util.Objects;
 
public class Student {
    private String name;
    private int age;
    private double height;
 
    public Student() {
    }
 
    public Student(String name, int age, double height) {
        this.name = name;
        this.age = age;
        this.height = height;
    }
 
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    public int getAge() {
        return age;
    }
 
    public void setAge(int age) {
        this.age = age;
    }
 
    public double getHeight() {
        return height;
    }
 
    public void setHeight(double height) {
        this.height = height;
    }
 
    @Override
    public String toString() {
        return '\n' + "名字：" + name + '\n' +
                "年龄：" + age + '\n' +
                "身高：" + height + '\n';
    }
 
    //只要两个对象内容一样，就返回true
    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Student student = (Student) o;
        return age == student.age && Double.compare(student.height, height) == 0 && Objects.equals(name, student.name);
    }
 
    //只要两个对象内容一样，返回的哈希值就一样
    @Override
    public int hashCode() {
        //根据名字 身高 年龄来计算哈希值
        return Objects.hash(name, age, height);
    }
}