如何实现 Java 可比接口？

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Implement Comparable<Animal> interface in your class and provide implementation of int compareTo(Animal other) method in your class.See This Post

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最佳答案

You just have to define that Animal implements Comparable<Animal> i.e. public class Animal implements Comparable<Animal>. And then you have to implement the compareTo(Animal other) method that way you like it.

@Override
public int compareTo(Animal other) {
return Integer.compare(this.year_discovered, other.year_discovered);
}

Using this implementation of compareTo, animals with a higher year_discovered will get ordered higher. I hope you get the idea of Comparable and compareTo with this example.

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You would need to implement the interface and define the compareTo() method. For a good tutorial go to - Tutorials point link or MyKongLink

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Use a Comparator...

    public class AnimalAgeComparator implements Comparator<Animal> {


@Override
public int compare(Animal a1, Animal a2) {
...
}
}

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You need to:

Add implements Comparable<Animal> to the class declaration; and
Implement a int compareTo( Animal a ) method to perform the comparisons.

Like this:

public class Animal implements Comparable<Animal>{
public String name;
public int year_discovered;
public String population;


public Animal(String name, int year_discovered, String population){
this.name = name;
this.year_discovered = year_discovered;
this.population = population;
}


public String toString(){
String s = "Animal name: "+ name+"\nYear Discovered: "+year_discovered+"\nPopulation: "+population;
return s;
}


@Override
public int compareTo( final Animal o) {
return Integer.compare(this.year_discovered, o.year_discovered);
}
}

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This thing can easily be done by implementing a public class that implements Comparable. This will allow you to use compareTo method which can be used with any other object to which you wish to compare.

for example you can implement it in this way:

public String compareTo(Animal oth)
{
return String.compare(this.population, oth.population);
}

I think this might solve your purpose.

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While you are in it, I suggest to remember some key facts about compareTo() methods

CompareTo must be in consistent with equals method e.g. if two objects are equal via equals() , there compareTo() must return zero otherwise if those objects are stored in SortedSet or SortedMap they will not behave properly.
CompareTo() must throw NullPointerException if current object get compared to null object as opposed to equals() which return false on such scenario.

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Possible alternative from the source code of Integer.compare method which requires API Version 19 is :

public int compareTo(Animal other) { return Integer.valueOf(this.year_discovered).compareTo(other.year_discovered); }

This alternative does not require you to use API version 19.

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Emp class needs to implement Comaparable interface so we need to Override its compateTo method.

import java.util.ArrayList;
import java.util.Collections;




class Emp implements Comparable< Emp >{


int empid;
String name;


Emp(int empid,String name){
this.empid = empid;
this.name = name;


}




@Override
public String toString(){
return empid+" "+name;
}


@Override
public int compareTo(Emp o) {


if(this.empid==o.empid){
return 0;
}
else if(this.empid < o.empid){
return 1;
}
else{
return -1;
}
}
}

public class JavaApplication1 {




public static void main(String[] args) {


ArrayList<Emp> a= new ArrayList<Emp>();


a.add(new Emp(10,"Mahadev"));
a.add(new Emp(50,"Ashish"));
a.add(new Emp(40,"Amit"));
Collections.sort(a);
for(Emp id:a){
System.out.println(id);
}
}


}