Java——hashMap去重和排序

Posted 2022-05-17 tractors

hashMap去重/排序：

　　1）map集合需要键名唯一，hashmap是通过hashcode和eauals来控制键名唯一；

　　2）从写Comparable中的compareTo方法来对map集合排序；

　　1、实体类：

public class Student implements Comparable<Student>
    private String name;
    private int age;
    public Student(String name, int age) 
        this.name = name;
        this.age = age;
    
    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 "Student" +
                "name=‘" + name + ‘\‘‘ +
                ", age=" + age +
                ‘‘;
    

    @Override
    public int compareTo(Student s) 
        int num = new Integer(this.getAge()).compareTo(new Integer(s.getAge()));
        if (num == 0) 
            num = this.getName().compareTo(s.getName());
        
        return num;
    

    @Override
    public int hashCode() 
        System.out.println(this.name+".....hashCode");
        return this.getName().hashCode();
    
    @Override
    public boolean equals(Object obj) 
        if (this == obj) return true;
        if (!(obj instanceof Student)) return false;
        Student s = (Student) obj;
        System.out.println(this.name+this.age+"..equals..");
        return this.getName().equals(s.getName()) && this.getAge() == s.getAge();
    

　　2、测试类；

public class Test 
    public static void main(String[] args) 
        Map<Student, String> ms = new HashMap<Student, String>();
        ms.put(new Student("张三", 10), "北京");
        ms.put(new Student("张五", 12), "南京");
        ms.put(new Student("张五", 12), "北京");
        ms.put(new Student("张五", 13), "北京");

        Set<Map.Entry<Student, String>> entries = ms.entrySet();
        for (Iterator<Map.Entry<Student, String>> it2 = entries.iterator(); it2.hasNext(); ) 
            Map.Entry<Student, String> next = it2.next();
            System.out.println(next.getKey() + "====" + next.getValue());