简单的理解java集合中的HashSet和HashTree几个重写方法

  public static void main(String[] args) {
    HashSet<String> set = new HashSet();
    set.add("java");
    set.add("c");
    set.add("php");
    set.add("bigdata");
    set.add("java");
    //运行结果，给去重了，而且是无序的
    System.out.println(set);//[java, c, bigdata, php]
  }
}

public class Demo1 {
  public static void main(String[] args) {
    HashSet<Person> set1 = new HashSet<>();
    set1.add(new Person("aing",50));
    set1.add(new Person("bing",10));
    set1.add(new Person("ding",20));
    set1.add(new Person("ding",20));
    //运行结果是即使名字年龄一样，也会输出两个，我们如果想要按照自己的规则去重，这样我们一定要重写hashcode 和euqals方法
    System.out.println(set1);//[Person{name='bing', age=10}, Person{name='ding', age=20}, Person{name='aing', age=50}, Person{name='ding', age=20}]
  }
}
class Person{
  String name;
  int age;

  public Person(String name, int age) {
    this.name = name;
    this.age = age;
  }

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

public class Demo1 {
  public static void main(String[] args) {
    HashSet<Person> set1 = new HashSet<>();
    set1.add(new Person("aing",50));
    set1.add(new Person("bing",10));
    set1.add(new Person("ding",20));
    set1.add(new Person("ding",20));
    //根据年龄和姓名比较的
    System.out.println(set1);//[Person{name='ding', age=20}, Person{name='aing', age=50}, Person{name='bing', age=10}]
  }
}
class Person{
  String name;
  int age;
  public Person(String name, int age) {
    this.name = name;
    this.age = age;
  }
  @Override
  public String toString() {
    return "Person{" +
        "name='" + name + '\'' +
        ", age=" + age +
        '}';
  }
  @Override
  public boolean equals(Object o) {
    if (this == o) return true;
    if (o == null || getClass() != o.getClass()) return false;
    Person person = (Person) o;
    return age == person.age &&
        Objects.equals(name, person.name);
  }
  //和属性关联，根据属性的值比较，之所以让age*100;是因为怕有可能出现这个name.hashCode()+age 和 下一个name.hashCode()+age加起来的值恰好相等，所以age*100,可以避免这种情况的发生
  @Override
  public int hashCode() {
    //return Objects.hash(name, age);
    return name.hashCode()+age*100;
  }
}

public class Demo2 {
  public static void main(String[] args) {
    TreeSet<String> set = new TreeSet();
    set.add("java");
    set.add("c");
    set.add("php");
    set.add("bigdata");
    set.add("java");
    System.out.println(set);//[bigdata, c, java, php]
  }
}

public class Demo2 {
  public static void main(String[] args) {
    TreeSet<Person1> set1 = new TreeSet<>();
    set1.add(new Person1("aing",50));
    set1.add(new Person1("bing",10));
    set1.add(new Person1("ding",20));
    set1.add(new Person1("ding",20));
    System.out.println(set1);
  }
}
class Person1{
  String name;
  int age;

  public Person1(String name, int age) {
    this.name = name;
    this.age = age;
  }

  @Override
  public String toString() {
    return "Person1{" +
        "name='" + name + '\'' +
        ", age=" + age +
        '}';
  }
}

public class Demo2 {
  public static void main(String[] args) {
    TreeSet<Person1> set1 = new TreeSet<>();
    set1.add(new Person1("aing",50));
    set1.add(new Person1("bing",10));
    set1.add(new Person1("ding",20));
    set1.add(new Person1("ding",20));
    System.out.println(set1);
  }
}
class Person1 implements Comparable{
  String name;
  int age;

  public Person1(String name, int age) {
    this.name = name;
    this.age = age;
  }

  @Override
  public boolean equals(Object o) {
    if (this == o) return true;
    if (o == null || getClass() != o.getClass()) return false;
    Person1 person1 = (Person1) o;
    return age == person1.age &&
        Objects.equals(name, person1.name);
  }

  @Override
  public int hashCode() {
    return name.hashCode()+age*100;
  }

  @Override
  public String toString() {
    return "Person1{" +
        "name='" + name + '\'' +
        ", age=" + age +
        '}';
  }
  //根据类的属性进行排序
  @Override
  public int compareTo(Object o) {
  Person1 person = (Person1)o;
  int num = name.compareTo(person.name);
  return num==0?age-person.age:num;
}
}