Java API提供了两种方法来排序：
java.util.Collections.sort(java.util.List)
java.util.Collections.sort(java.util.List, java.util.Comparator)
一、Collections.sort（List list）
使用此API排序，要求javabean实现Comparable接口
Dog类：
public class Dog implements Comparable<Dog> {
private String name;
private int age;
public Dog(String name, int age) {
this.name = name;
this.age = age;
}
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;
}
/**
* 如果比较的是字符串，则使用String.CompareTo(String s)方法
*/
// @Override
// public int compareTo(Dog dog) {
// return this.getName().compareTo(dog.getName());
// }
/**
* 比较int型和char型
*/
@Override
public int compareTo(Dog dog) {
return this.age - dog.age;
}
}
测试类：
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
public class Test {
public static void main(String[] args) {
List<Dog> mDogs = new ArrayList<>();
Dog dog1 = new Dog("eog4", 4);
Dog dog2 = new Dog("dog5", 5);
Dog dog3 = new Dog("bog2", 2);
Dog dog4 = new Dog("cog3", 3);
Dog dog5 = new Dog("aog1", 1);
mDogs.add(dog1);
mDogs.add(dog2);
mDogs.add(dog3);
mDogs.add(dog4);
mDogs.add(dog5);
System.out.println("排序之前：");
for (Dog dog : mDogs) {
System.out.println(dog.getName());
}
// 排序
Collections.sort(mDogs);
System.out.println("排序之后：");
for (Dog dog : mDogs) {
System.out.println(dog.getName());
}
}
}
测试结果：
排序之前：
eog4
dog5
bog2
cog3
aog1
排序之后：
aog1
bog2
cog3
eog4
dog5
二、Collections.sort（List list，Comparator<T> comparator）
使用此API实现排序，需要实例化Comparator对象，重写compare(Object o1,Object o2）方法
Dog类：
public class Dog {
private String name;
private int age;
public Dog(String name, int age) {
this.name = name;
this.age = age;
}
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;
}
}
Test测试类：
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
public class Test {
public static void main(String[] args) {
List<Dog> mDogs = new ArrayList<>();
Dog dog1 = new Dog("eog4", 4);
Dog dog2 = new Dog("dog5", 5);
Dog dog3 = new Dog("bog2", 2);
Dog dog4 = new Dog("cog3", 3);
Dog dog5 = new Dog("aog1", 1);
mDogs.add(dog1);
mDogs.add(dog2);
mDogs.add(dog3);
mDogs.add(dog4);
mDogs.add(dog5);
Comparator<Dog> comparator = new Comparator<Dog>() {
@Override
public int compare(Dog o1, Dog o2) {
return o2.getAge() - o1.getAge();
}
};
System.out.println("排序之前：");
for (Dog dog : mDogs) {
System.out.println(dog.getName());
}
// 排序
Collections.sort(mDogs,comparator);
System.out.println("排序之后：");
for (Dog dog : mDogs) {
System.out.println(dog.getName());
}
}
}
测试结果：
排序之前：
eog4
dog5
bog2
cog3
aog1
排序之后：
dog5
eog4
cog3
bog2
aog1
如果对String属性排序，使用String.CompareTo(String s)方法进行排序
@Override
public int compareTo(Dog o) {
return this.name.compareTo(o.getName());
}
三、对数组进行排序
如果数组或集合元素是String类型，则可以利用Java API实现的Comparator<String>对象String.CASE_INSENSITIVE_ORDER为容器元素排序。
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
public class Test {
public static void main(String[] args) {
String[] array=new String[]{"c","b","d","a","e"};
List<String> list=Arrays.asList(array);
System.out.println("排序之前：");
for (String string : list) {
System.out.println(string);
}
Collections.sort(list,String.CASE_INSENSITIVE_ORDER);
System.out.println("排序之后：");
for (String string : list) {
System.out.println(string);
}
Collections.sort(list,Collections.reverseOrder());
System.out.println("反序：");
for (String string : list) {
System.out.println(string);
}
}
}
测试结果：
排序之前：
c
b
d
a
e
排序之后：
a
b
c
d
e
反序：
e
d
c
b
a
