Java 入门 37 Set系列集合的特点 集合工具类Collections 综合案例 Map集合体系 集合的嵌套

 

 

 

package com.ITheima._set;

import java.util.HashSet;
import java.util.LinkedHashSet;
import java.util.Set;
 
public class SetDemo {
    public static void main(String[] args) {
        // 看看Set系列集合的特点： HashSet LinkedHashSet TreeSet
        //
        Set<String> sets=new HashSet<>();//一行经典代码 无序不重复 五索引
        //Set<String> sets=new LinkedHashSet<>();//有序不重复 无索引
        sets.add("HTML");
        sets.add("MYSQL");
        sets.add("Java");
        sets.add("SpringBot");
        System.out.println(sets);//[Java, MYSQL, HTML, SpringBot]
    }
}

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package com.ITheima._set;

public class SetDemo1 {
    public static void main(String[] args) {
        // 目标：学会获取对象的哈希值，并确认一下
        String name = "itheima";
        System.out.println(name.hashCode());//2118746965
        System.out.println(name.hashCode());//2118746965

        String name1 = "itheima1";
        System.out.println(name1.hashCode());//1256646524
        System.out.println(name1.hashCode());//1256646524
    }
}

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 案例

 

 Student类  重写 hasCode equals 方法

package com.ITheima._set;

import java.util.Objects;

public class Student {
    private String name;
    private int age;
    private char sex;

    public Student() {
    }

    public Student(String name, int age, char sex) {
        this.name = name;
        this.age = age;
        this.sex = sex;
    }

    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 char getSex() {
        return sex;
    }

    public void setSex(char sex) {
        this.sex = sex;
    }

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", sex=" + sex +
                '}';
    }

    @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 && sex == student.sex && Objects.equals(name, student.name);
    }

    @Override
    public int hashCode() {
        return Objects.hash(name, age, sex);
    }
}

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 SetDemo3类 

package com.ITheima._set;

import java.util.HashSet;
import java.util.Set;

/**
 * 目标：让Set集合把重复内容的对象去掉一个（去重复）
 */
public class SetDemo3 {
    public static void main(String[] args) {
        // Set集合去重复原因：先判断哈希值算出来的存储位置是否相同 再判断equals
        Set<Student> sets = new HashSet<>();

        Student s1 = new Student("无恙", 20, '男');
        Student s2 = new Student("无恙", 20, '男');
        Student s3 = new Student("周雄", 21, '男');
        //必须重写 hasCode equals 两个方法(才能保证不会出现重复)
        System.out.println(s1.hashCode());//685325104
        System.out.println(s2.hashCode());//460141958
        System.out.println(s3.hashCode());//1163157884

        sets.add(s1);
        sets.add(s2);
        sets.add(s3);

        System.out.println(sets);

    }
}

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标签：Map,Set,name,age,sex,Student,sets,集合,public
来源： https://www.cnblogs.com/lvlisn/p/16425442.html