java中Comparable接口

阳光穿透心脏的1/2处 2022-04-06 09:40 290阅读 0赞

# java中Comparable接口 #

所有可以排序的类，都实现了java.lang.Comparable接口。

Comparable中只有一个方法：

int conpareTo(T o)

返回0，表示this == obj

返回正数，表示this > obj

返回负数，表示this < obj

BasicContainer2.java

import java.util.*;
    
    public class BasicContainer2 {
        public static void main(String[] args) {
    		List l1 = new LinkedList();
    		l1.add(new Name("Karl","M"));
    		l1.add(new Name("Steven","Lee"));
    		l1.add(new Name("John","O"));
    		l1.add(new Name("Tom","M"));
    		System.out.println(l1);//[Karl M, Steven Lee, John O, Tom M]
    		
    		//调用sort方法排序
    		//排序之前必须重写compaerTo比较大小，否则无效
    		Collections.sort(l1);
    		System.out.println(l1);//[Steven Lee, Karl M, Tom M, John O]
    		
        }
    }
    
    //实现Comparable接口
    class Name implements Comparable {
        private String firstName,lastName;
        public Name(String firstName, String lastName) {
            this.firstName = firstName; this.lastName = lastName;
        }
        public String getFirstName() {  return firstName;   }
        public String getLastName() {   return lastName;   }
        public String toString() {  return firstName + " " + lastName;  }
        
        public boolean equals(Object obj) {
    	    if (obj instanceof Name) {
    	        Name name = (Name) obj;
    	        return (firstName.equals(name.firstName))
    	            && (lastName.equals(name.lastName));
    	    }
    	    return super.equals(obj);
    		}
    		
    	public int hashCode() {
    		return firstName.hashCode();
    	}
    		
    	//改写Comparable的compareTo方法	
    	public int compareTo(Object o) {
    		Name n = (Name)o;
    		//调用String类的compareTo方法，比较大小
    		int lastCmp = lastName.compareTo(n.lastName);
    		//lastCmp,首先按照姓（lastName）排列，然后按照名（fisrtName）排列
    		return (lastCmp!=0 ? lastCmp : firstName.compareTo(n.firstName));
    	}
    		
    }

F:\java>javac BasicContainer2.java
    注: BasicContainer2.java使用了未经检查或不安全的操作。
    注: 有关详细信息, 请使用 -Xlint:unchecked 重新编译。
    
    F:\java>java BasicContainer2
    [Karl M, Steven Lee, John O, Tom M]
    [Steven Lee, Karl M, Tom M, John O]
    
    F:\java>