Java集合Set与Collections案例详解

public class SetTest1 {
    public static void main(String[] args) {
        // 创建一个Set集合的对象
        /**
         * HashSet的集合, 是一行经典代码(常用) 特点: 无序不重复 无索引
         * 针对无序不是每次都是随机的, 第一次无序排好之后, 以后都是这个顺序(面试题)
         */
        // Set<Integer> set = new HashSet<>();
        // 特点: 有序、无索引、不重复
        // Set<Integer> set = new LinkedHashSet<>();
        // 可排序(默认升序)、无索引、不重复
        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 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;
    }
​
    // 自己提供Getter 和 Setter方法 以及toString方法
    @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(height, student.height) == 0 && Objects.equals(name, student.name);
    }
​
    @Override
    public int hashCode() {
        int result = name != null ? name.hashCode() : 0;
        result = 31 * result + age;
        return result;
    }
}
​
public class SetTest2 {
    public static void main(String[] args) {
        // 哈希值不相同
        Student s1 = new Student("柳岩", 18, 163);
        Student s2 = new Student("宝强", 18, 163);
        System.out.println(s1.hashCode());
        System.out.println(s1.hashCode());
        System.out.println(s2.hashCode());
​
        System.out.println("----------------------");
​
        // 哈希值相同
        String str1 = new String("abc");
        String str2 = new String("acD");
        System.out.println(str1.hashCode());
        System.out.println(str2.hashCode());
    }
}

public class Student{
    private String name; //姓名
    private int age; //年龄
    private double height; //身高
    //无参数构造方法
    public Student(){}
    //全参数构造方法
    public Student(String name, int age, double height){
        this.name=name;
        this.age=age;
        this.height=height;
    }
    //...get、set、toString()方法自己补上..
    // 按快捷键生成hashCode和equals方法
    // alt+insert 选择 hashCode and equals
    // 只要两个对象的内容一样就会返回true
    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
​
        Student student = (Student) o;
​
        if (age != student.age) return false;
        if (Double.compare(student.height, height) != 0) return false;
        return name != null ? name.equals(student.name) : student.name == null;
    }
​
    // 只要两个对象内容一样, 返回的哈希值就是一样的
    @Override
    public int hashCode() {
        // 根据姓名  年龄  身高计算哈希值
        return Objects.hash(name, age, height);
    }
}

public class SetTest3 {
    public static void main(String[] args) {
        Set<Student> students = new HashSet<>();
        Student s1 = new Student("至尊宝",20, 169.6);
        Student s2 = new Student("蜘蛛精",23, 169.6);
        Student s3 = new Student("蜘蛛精",23, 169.6);
        Student s4 = new Student("牛魔王",48, 169.6);
        System.out.println(s2.hashCode());
        System.out.println(s3.hashCode());
​
        students.add(s1);
        students.add(s2);
        students.add(s3);
        students.add(s4);
​
        for(Student s : students){
            System.out.println(s);
        }
    }
}

public class SetTest4 {
    public static void main(String[] args) {
        Set<Student> students = new LinkedHashSet<>();
        Student s1 = new Student("至尊宝",20, 169.6);
        Student s2 = new Student("蜘蛛精",23, 169.6);
        Student s3 = new Student("蜘蛛精",23, 169.6);
        Student s4 = new Student("牛魔王",48, 169.6);
​
        students.add(s1);
        students.add(s2);
        students.add(s3);
        students.add(s4);
​
        for(Student s : students){
            System.out.println(s);
        }
    }
}