TreeSet的排序两种实现方式Comparator和Comparable

待我称王封你为后i 2022-07-24 11:15 129阅读 0赞

TreeSet

条件

类型一样

设计到排序

comparable是自然（可以修改类的情况下）

comparator是定制（不可以修改类的情况下）优先级更高

使用说明：

一般采用的是自然排序，但是当，不能对类进行修改时不得不采用comparator方法，下面的demo采用了两种方式结合。

代码整体说明：

Employee类的birthday属性是自定义类MyDate类型

Employee采用comparable方式默认的是按着姓名进行排序

然后采用定制的Comparator方式对出生日期进行排序

package TestContainer;
    
    public class MyDate {
    	private int day;
    	private int month;
    	private int year;
    
    	public int getDay() {
    		return day;
    	}
    
    	public void setDay(int day) {
    		this.day = day;
    	}
    
    	public int getMonth() {
    		return month;
    	}
    
    	public void setMonth(int month) {
    		this.month = month;
    	}
    
    	public int getYear() {
    		return year;
    	}
    
    	@Override
    	public int hashCode() {
    		final int prime = 31;
    		int result = 1;
    		result = prime * result + day;
    		result = prime * result + month;
    		result = prime * result + year;
    		return result;
    	}
    
    	@Override
    	public boolean equals(Object obj) {
    		if (this == obj)
    			return true;
    		if (obj == null)
    			return false;
    		if (getClass() != obj.getClass())
    			return false;
    		MyDate other = (MyDate) obj;
    		if (day != other.day)
    			return false;
    		if (month != other.month)
    			return false;
    		if (year != other.year)
    			return false;
    		return true;
    	}
    
    	public void setYear(int year) {
    		this.year = year;
    	}
    
    	public MyDate(int day, int month, int year) {
    		super();
    		this.day = day;
    		this.month = month;
    		this.year = year;
    	}
    
    	public MyDate() {
    		super();
    	}
    
    	@Override
    	public String toString() {
    		return "MyDate [day=" + day + ", month=" + month + ", year=" + year + "]";
    	}
    
    }

package TestContainer;
    //是否重写compareTo()和equals()方法
    //虽然比较的是String或者Integer的compareTo()方法，但是，把Employee放到TreeSet中还需要判断多个Employee是否相等
    public class Employee implements Comparable{
    	private String name;
    	@Override
    	public int hashCode() {
    		final int prime = 31;
    		int result = 1;
    		result = prime * result + age;
    		result = prime * result + ((birthday == null) ? 0 : birthday.hashCode());
    		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;
    		Employee other = (Employee) obj;
    		if (age != other.age)
    			return false;
    		if (birthday == null) {
    			if (other.birthday != null)
    				return false;
    		} else if (!birthday.equals(other.birthday))
    			return false;
    		if (name == null) {
    			if (other.name != null)
    				return false;
    		} else if (!name.equals(other.name))
    			return false;
    		return true;
    	}
    
    	private int age;
    	private MyDate birthday;
    
    	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 MyDate getBirthday() {
    		return birthday;
    	}
    
    	public void setBirthday(MyDate birthday) {
    		this.birthday = birthday;
    	}
    
    	public Employee() {
    		super();
    	}
    
    	public Employee(String name, int age, MyDate birthday) {
    		super();
    		this.name = name;
    		this.age = age;
    		this.birthday = birthday;
    	}
    
    	@Override
    	public String toString() {
    		return "Employee [name=" + name + ", age=" + age + ", birthday=" + birthday + "]";
    	}
    
    	@Override
    	public int compareTo(Object o) {
    		if(o instanceof Employee){
    			Employee employee=(Employee)o;
    			int i=this.getName().compareTo(employee.getName());
    //			if(i==0){
    //				int j=this.getAge()-employee.getAge();
    				if (j==0){
    					
    				}
    //				return j;
    //			}
    			return i;
    		}
    		return 0;
    	}
    }

package TestContainer;
    
    import static org.junit.Assert.*;
    
    import java.util.Comparator;
    import java.util.TreeSet;
    
    import org.junit.Test;
    
    public class TestEmployee {
    
    	// 自然排序,Employee实现Comparable接口，并按着Name排序
    	@Test
    	public void test() {
    		Employee e1 = new Employee("Haid", 31, new MyDate(2, 2, 1985));
    		Employee e2 = new Employee("Qiao", 25, new MyDate(13, 10, 1991));
    		Employee e3 = new Employee("Alex", 20, new MyDate(2, 2, 1996));
    		Employee e4 = new Employee("Tom", 37, new MyDate(2, 2, 1980));
    		Employee e5 = new Employee("Alex", 28, new MyDate(13, 10, 1989));
    
    		// 定制排序Comparator
    		Comparator comparator = new Comparator() {
    			public int compare(Object o1, Object o2) {
    				if (o1 instanceof Employee && o2 instanceof Employee) {
    					Employee e1 = (Employee) o1;
    					Employee e2 = (Employee) o2;
    					int i = e1.getBirthday().getYear() - e2.getBirthday().getYear();
    					if (i == 0) {
    						int j = e1.getBirthday().getMonth() - e2.getBirthday().getMonth();
    						if (j == 0) {
    							return e1.getBirthday().getDay() - e2.getBirthday().getDay();
    						}
    						return j;
    					}
    					return i;
    				}
    				return 0;
    
    			}
    
    		};
    
    		TreeSet set = new TreeSet(comparator);
    		set.add(e1);
    		set.add(e2);
    		set.add(e3);
    		set.add(e4);
    		set.add(e5);
    
    		for (Object object : set)
    			System.out.println(object);
    
    	}
    }