J2EE集合框架之set-阿里云开发者社区

一. set集和的特点：

1.set集合是无序的没有下标所以没有修改的方法：

2. 不可重复对象

foreach

迭代器

三、Set去重原理

代码测试

输出结果

四、Set 排序

1.自然排序接口

2.比较器排序接口

一. set集和的特点：

set集合是无序的没有下标所以没有修改的方法：

1. 不可重复对象

输出结果：

二、Set遍历

foreach

输出结果：

迭代器

输出结果：

三、Set去重原理：

先比较hashCode再比较equals，set集合去重底层是调用hashCode方法以及equals，如果hashCode相等就会调用equals方法，如果不同的话就不会调用

去重是要先经过hashCode的值来筛选，如果两个值都相等的话就会被判定为同一个对象

代码测试：

package com.xiaoye.xy;
import java.util.HashSet;
public class xy3 {
public static void main(String[] args) {
  HashSet h=new HashSet<>();
  h.add(new qc(1,"xg",15));
  h.add(new qc(2,"xy",18));
  h.add(new qc(3,"xh",16));
  h.add(new qc(4,"xz",12));
  System.out.println(h.contains(new qc(2,"xy",18)));
  }
}
class qc{
  private int id;
  private String name;
  private int age;
  public int getId() {
    return id;
  }
  public void setId(int id) {
    this.id = id;
  }
  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;
  }
  @Override
  public String toString() {
    return "qc [id=" + id + ", name=" + name + ", age=" + age + "]";
  }
  public qc(int id, String name, int age) {
    super();
    this.id = id;
    this.name = name;
    this.age = age;
  }
  public qc() {
    super();
  }
  @Override
  public int hashCode() {
    System.out.println("hashCode被调用了");
    final int prime = 31;
    int result = 1;
    result = prime * result + age;
    result = prime * result + id;
    result = prime * result + ((name == null) ? 0 : name.hashCode());
    return result;
  }
  @Override
  public boolean equals(Object obj) {
    System.out.println("equals被调用了");
    if (this == obj)
      return true;
    if (obj == null)
      return false;
    if (getClass() != obj.getClass())
      return false;
    qc other = (qc) obj;
    if (age != other.age)
      return false;
    if (id != other.id)
      return false;
    if (name == null) {
      if (other.name != null)
        return false;
    } else if (!name.equals(other.name))
      return false;
    return true;
  }
}

输出结果：

四、Set 排序

1.自然排序接口

this比较元素对象是进行升序
元素对象比较this的进行降序

package com.xiaoye.xy;
import java.util.HashSet;
public class xy3 {
public static void main(String[] args) {
  HashSet h=new HashSet<>();
  h.add(new qc(1,"xg",15));
  h.add(new qc(2,"xy",18));
  h.add(new qc(3,"xh",16));
  h.add(new qc(4,"xz",12));
  System.out.println(h.contains(new qc(2,"xy",18)));
  }
}
class qc{
  private int id;
  private String name;
  private int age;
  public int getId() {
    return id;
  }
  public void setId(int id) {
    this.id = id;
  }
  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;
  }
  @Override
  public String toString() {
    return "qc [id=" + id + ", name=" + name + ", age=" + age + "]";
  }
  public qc(int id, String name, int age) {
    super();
    this.id = id;
    this.name = name;
    this.age = age;
  }
  public qc() {
    super();
  }
  @Override
  public int hashCode() {
    System.out.println("hashCode被调用了");
    final int prime = 31;
    int result = 1;
    result = prime * result + age;
    result = prime * result + id;
    result = prime * result + ((name == null) ? 0 : name.hashCode());
    return result;
  }
  @Override
  public boolean equals(Object obj) {
    System.out.println("equals被调用了");
    if (this == obj)
      return true;
    if (obj == null)
      return false;
    if (getClass() != obj.getClass())
      return false;
    qc other = (qc) obj;
    if (age != other.age)
      return false;
    if (id != other.id)
      return false;
    if (name == null) {
      if (other.name != null)
        return false;
    } else if (!name.equals(other.name))
      return false;
    return true;
  }
}

输出结果：

这样写会报一个Java.lang.comparable的错是因为实现类后面被存放的对象没有实现implements comparable

正确写法：要是现 implements Comparable<Person>

class Person implements Comparable<Person>{

在进行了排序后代码如下：

package com.xiaoye.xy;
import java.util.HashSet;
import java.util.TreeSet;
public class xy4 {
public static void main(String[] args) {
  HashSet h=new HashSet<>();
  h.add(new Person(1,13,"xn",12344));
  h.add(new Person(2,15,"xb",12533));
  h.add(new Person(3,16,"xc",15466));
  h.add(new Person(4,18,"xv",16767));
  h.add(new Person(5,19,"xr",46573));
  //默认排序
  for (Object object : h) {
    System.out.println(object);
  }
  TreeSet t=new TreeSet<>();
  //对数据进行加工
  for (Object object : h) {
    t.add(object);
  }
  System.out.println("----------------------------------------");
  for (Object object : t) {
    System.out.println(object);
  }
}
}
class Person implements Comparable<Person>{
  private int id;
  private int age;
  private String name;
  private int money;
  public int getId() {
    return id;
  }
  public void setId(int id) {
    this.id = id;
  }
  public int getAge() {
    return age;
  }
  public void setAge(int age) {
    this.age = age;
  }
  public String getName() {
    return name;
  }
  public void setName(String name) {
    this.name = name;
  }
  public int getMoney() {
    return money;
  }
  public void setMoney(int money) {
    this.money = money;
  }
  @Override
  public int hashCode() {
    final int prime = 31;
    int result = 1;
    result = prime * result + age;
    result = prime * result + id;
    result = prime * result + money;
    result = prime * result + ((name == null) ? 0 : name.hashCode());
    return result;
  }
  @Override
  public boolean equals(Object obj) {
    if (this == obj)
      return true;
    if (obj == null)
      return false;
    if (getClass() != obj.getClass())
      return false;
    Person other = (Person) obj;
    if (age != other.age)
      return false;
    if (id != other.id)
      return false;
    if (money != other.money)
      return false;
    if (name == null) {
      if (other.name != null)
        return false;
    } else if (!name.equals(other.name))
      return false;
    return true;
  }
  @Override
  public String toString() {
    return "Person [id=" + id + ", age=" + age + ", name=" + name + ", money=" + money + "]";
  }
  public Person(int id, int age, String name, int money) {
    super();
    this.id = id;
    this.age = age;
    this.name = name;
    this.money = money;
  }
  public Person() {
    super();
  }
  @Override
  public int compareTo(Person o) {
    // TODO Auto-generated method stub
    return this.id - o.id;
  }
}

输出结果：

2.比较器排序接口代码如下：

this比较元素对象是进行升序
元素对象比较this的进行降序

package com.xiaoye.xy;
import java.util.Comparator;
import java.util.HashSet;
import java.util.TreeSet;
public class xy4 {
public static void main(String[] args) {
  HashSet h=new HashSet<>();
  h.add(new Person(1,13,"xn",12344));
  h.add(new Person(2,15,"xb",12533));
  h.add(new Person(3,16,"xc",15466));
  h.add(new Person(4,18,"xv",16767));
  h.add(new Person(5,19,"xr",46573));
TreeSet t2=new TreeSet<>(new Comparator<Person>() {
    @Override
    public int compare(Person o1, Person o2) {
      // TODO Auto-generated method stub
      return o2.getMoney()-o1.getMoney();
    }
  });
  for (Object object : h) {
    t2.add(object);
  }
  for (Object object : t2) {
    System.out.println(object);
  }
System.out.println("----------------------------------------");
  TreeSet t3=new TreeSet<>(new Comparator<Person>() {
    @Override
    public int compare(Person o1, Person o2) {
      int xy=o2.getMoney()-o1.getMoney();
      if(xy==0) {
        return  o1.getAge()-o2.getAge();
      }
      return xy;
    }
  });
  for (Object object : h) {
    t3.add(object);
  }
  for (Object object : t3) {
    System.out.println(object);
  }
}
}
class Person implements Comparable<Person>{
  private int id;
  private int age;
  private String name;
  private int money;
  public int getId() {
    return id;
  }
  public void setId(int id) {
    this.id = id;
  }
  public int getAge() {
    return age;
  }
  public void setAge(int age) {
    this.age = age;
  }
  public String getName() {
    return name;
  }
  public void setName(String name) {
    this.name = name;
  }
  public int getMoney() {
    return money;
  }
  public void setMoney(int money) {
    this.money = money;
  }
  @Override
  public int hashCode() {
    final int prime = 31;
    int result = 1;
    result = prime * result + age;
    result = prime * result + id;
    result = prime * result + money;
    result = prime * result + ((name == null) ? 0 : name.hashCode());
    return result;
  }
  @Override
  public boolean equals(Object obj) {
    if (this == obj)
      return true;
    if (obj == null)
      return false;
    if (getClass() != obj.getClass())
      return false;
    Person other = (Person) obj;
    if (age != other.age)
      return false;
    if (id != other.id)
      return false;
    if (money != other.money)
      return false;
    if (name == null) {
      if (other.name != null)
        return false;
    } else if (!name.equals(other.name))
      return false;
    return true;
  }
  @Override
  public String toString() {
    return "Person [id=" + id + ", age=" + age + ", name=" + name + ", money=" + money + "]";
  }
  public Person(int id, int age, String name, int money) {
    super();
    this.id = id;
    this.age = age;
    this.name = name;
    this.money = money;
  }
  public Person() {
    super();
  }
  @Override
  public int compareTo(Person o) {
    // TODO Auto-generated method stub
    return this.id - o.id;
  }

输出结果：

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J2EE集合框架之set

一. set集和的特点：

三、Set去重原理

四、Set 排序

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