Question

如何在java里面对Object的类型值进行一个大小的比较

Answer 1

作者：Tao Li
链接：https://www.zhihu.com/question/36897771/answer/69763955
来源：知乎
著作权归作者所有。商业转载请联系作者获得授权，非商业转载请注明出处。

java中类的比较一般有两种方法，一种就是类本身实现Comparable<T>这个接口，比如通过对用户的姓名进行比较排序：

package com.ailot.compare;

public class User implements Comparable<User> {

private String name;
private int age;
private String sex;

public User(String name,int age,String sex){
this.name = name;
this.age = age;
this.sex = sex;
}
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 String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}

@Override
public String toString() {
return "User [name=" + name + ", age=" + age + ", sex=" + sex + "]";
}

@Override
public int compareTo(User u) {
// TODO Auto-generated method stub
int c = this.name.compareTo(u.name);
if(c==0){
return 0;
}else if(c > 0){
return 1;
}else{
return -1;
}
}
}

Test.java

package com.ailot.compare;

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

public class Test {

public static void main(String[] args) {
List<User> userList = new ArrayList<User>();
for(int i=0;i<10;i++){
int s = new Random().nextInt(20);
User u = new User(s+"张三",i,"男");
userList.add(u);
}
Collections.sort(userList);
for(User user : userList){
System.out.println(user.toString());
}
}

}

排序的话直接用 Collections.sort( userList ) ;就可以了。
作者：Tao Li
链接：https://www.zhihu.com/question/36897771/answer/69763955
来源：知乎
著作权归作者所有。商业转载请联系作者获得授权，非商业转载请注明出处。

另一种就是类没有实现Comparable<T>这个接口，这就需要自己新建一个比较的类，通过实现Comparator<T>来对类进行比较，还是对User类的姓名进行比较排序：

User.java

package com.ailot.compare;

public class User {

private String name;
private int age;
private String sex;

public User(String name,int age,String sex){
this.name = name;
this.age = age;
this.sex = sex;
}

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 String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}

@Override
public String toString() {
return "User [name=" + name + ", age=" + age + ", sex=" + sex + "]";
}
}

UserCompare.java

package com.ailot.compare;

import java.util.Comparator;

public class UserCompare implements Comparator<User> {

@Override
public int compare(User u1, User u2) {
// TODO Auto-generated method stub
int c = u1.getName().compareTo(u2.getName());
if(c == 0){
return 0;
}else if(c < 0){
return -1;
}else{
return 1;
}
}

}

Test.java

package com.ailot.compare;

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

public class Test {

public static void main(String[] args) {
List<User> userList = new ArrayList<User>();
for(int i=0;i<10;i++){
int s = new Random().nextInt(20);
User u = new User(s+"张三",i,"男");
userList.add(u);
}
Collections.sort(userList,new UserCompare());
for(User user : userList){
System.out.println(user.toString());
}
}

}

排序的话直接用 Collections.sort(userList,new UserCompare());就可以了。

Answer 2

这个类是什么样的类，比较类的对象，一般比较的是对象的属性，这样的话就可以在类里面写个CompareTo（XXXX)方法，把两个对象的属性按你想要的规则进行比较就行了，返回值的话建议返回-1，0，1