比较器 comparable vs comparator

comparable

比较this和其他对象实例，类需实现（implements）java.lang.Comparable接口，重写public int compareTo(Object o1)

comparator

比较2个不同的对象实例，比较器类需实现（implements）java.util.Comparator接口，重写public int compare(Object o1, Object o2)

java.lang.Comparable:int compareTo(Object o1)

比较this Object 和 o1 Object

返回值意义：

1.正数—this Object 大于 o1

2.负数—this Object 小于 o1

3.0—this Object 等于 o1

在排序中，如果当前对象实例this某字段大于 o1某字段，返回正数，即按从小到大排序（正序）；

int compareTo(Employee o1){
if (this.age > o1.age) {
return 1;
} else if (this.age < o1.age) {
return -1;
} else {
return 0;
}
}

java.util.Comparator:int compare(Object o1, Object o2)

比较o1 object 和 o2 object

返回值意义：

1.正数—o1 大于 o2

2.负数—o2 小于 o2

3.0—o1 等于 o2

当o1.getSalary() 大于 o2.getSalary()，返回正数，则从小到大输出（正序）；依此类推

//根据对象实例的Salary从小到大
public int compare(Employee o1, Employee o2) {
// TODO Auto-generated method stub
if(o1.getSalary() > o2.getSalary()){
return 1;
}else if(o1.getSalary() < o2.getSalary()){
return -1;
}else{
return 0;
}
}

区别:

comparable	comparator
Defined in java.lang.comparable	Definded in java.util.comparator
override public int compareTo(Object o1)	override public int compare(Object o1, Object 02)
java.util.Collections.sort(List) and java.util.Arrays.sort(Object[])	java.util.Collections.sort(List, Comparator) and java.util.Arrays.sort(Object[], Comparator)
Class whose objects to be sorted must implement this interface	Class whose objects to be sorted do not need to implement this interface

代码实例：

comparable接口

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

class Human implements Comparable<Human> {

private String name;
private int age;
private double height;

public Human(String name, int age, double height) {
this.name = name;
this.age = age;
this.height = height;
}

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 double getHeight() {
return height;
}

public void setHeight(double height) {
this.height = height;
}

// 年龄从小到大
@Override
public int compareTo(Human o) {
// TODO Auto-generated method stub
if (this.age > o.age) {
return 1;
} else if (this.age < o.age) {
return -1;
} else {
return 0;
}

}
}

public class TestHumanSort {

private static void printList(List<Human> list) {
System.out.println("name\tage\theight");
for (Human hm : list) {
System.out.println(hm.getName() + "\t" + hm.getAge() + "\t"
+ hm.getHeight());
}
}

public static void main(String[] args) {
List<Human> testHumanList = new ArrayList<Human>();
testHumanList.add(new Human("Bill", 16, 175));
testHumanList.add(new Human("John", 18, 170));
testHumanList.add(new Human("Jack", 15, 180));

Collections.sort(testHumanList);
printList(testHumanList);

}
}

输出：

name    age height
Jack    15  180.0
Bill    16  175.0
John    18  170.0

comparator接口

import java.util.Comparator;

public class EmpSortBySalary implements Comparator<Employee>{

@Override
public int compare(Employee o1, Employee o2) {
// TODO Auto-generated method stub
if(o1.getSalary() > o2.getSalary()){
return 1;
}else if(o1.getSalary() < o2.getSalary()){
return -1;
}else{
return 0;
}

}

}

主函数：

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

class Employee{
private String name;
private int age;
private long salary;

public Employee(String name, int age, long salary){
this.name = name;
this.age = age;
this.salary = salary;
}
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 long getSalary() {
return salary;
}
public void setSalary(long salary) {
this.salary = salary;
}
}

public class TestEmployeeSort {

private static void printList(List<Employee> list) {
System.out.println("name\tage\tsalary");
for (Employee ey : list) {
System.out.println(ey.getName() + "\t" + ey.getAge() + "\t"
+ ey.getSalary());
}
}

public static void main(String[] args) {
// TODO Auto-generated method stub
List<Employee> emList = new ArrayList<Employee>();
emList.add(new Employee("Jack", 28, 10000));
emList.add(new Employee("John", 60, 3000));
emList.add(new Employee("Bill", 50, 20000));

Collections.sort(emList, new EmpSortBySalary());

printList(emList);

}

}

输出

name    age salary
John    60  3000
Jack    28  10000
Bill    50  20000