Java工具类中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)
package cn.mtianyan.sort;
public class Cat implements Comparable{
private String name; //名字
private int month; //年龄
private String species;//品种
@Override
public String toString() {
return "[姓名：" + name + ", 年龄：" + month + ", 品种：" + species + "]";
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getMonth() {
return month;
}
public void setMonth(int month) {
this.month = month;
}
public String getSpecies() {
return species;
}
public void setSpecies(String species) {
this.species = species;
}
public Cat(String name, int month, String species) {
this.name = name;
this.month = month;
this.species = species;
}
@Override
public int compareTo(Object o) {
return this.month-((Cat)o).month;
}
}
package cn.mtianyan.sort;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
public class CatTest{
public static void main(String[] args) {
List<Cat> list = new ArrayList<>();
// 定义宠物猫对象
Cat huahua = new Cat("花花", 12, "英国短毛猫");
Cat fanfan = new Cat("凡凡", 3, "中华田园猫");
Cat huahua02 = new Cat("花花二代", 2, "英国短毛猫");
list.add(huahua);
list.add(fanfan);
list.add(huahua02);
System.out.println("排序前宠物猫信息");
for (Cat cat: list) {
System.out.println(cat);
}
// 执行排序操作
Collections.sort(list); // Cat必须实现Comparable接口，并实现其方法
System.out.println("按年龄从大到小排序之后宠物猫信息");
for (Cat cat: list) {
System.out.println(cat);
}
}
}
使用Collection.sort方法来进行排序，被排序对象必须实现Comparable接口，并重写compareTo方法
@Override
public int compareTo(Object o) {
return this.month-((Cat)o).month;
}
将此对象与指定的对象进行比较以进行排序。 返回一个负整数，零或正整数，分别对应该对象小于，等于或大于指定对象。
比如猫的例子，第一个12与第二个3进行比较。12-3=9是大于的。
下图提示语有错误: 应该为从小到大。
名字字符串排序
@Override
public int compareTo(Object o) {
return ((Cat)o).name.compareTo(this.name);
}
// 定义宠物猫对象
Cat huahua = new Cat("aa", 12, "英国短毛猫");
Cat fanfan = new Cat("bb", 3, "中华田园猫");
Cat huahua02 = new Cat("cc", 2, "英国短毛猫");
运行结果:
Collections.sort(List list, Comparator<T> comparator)
package cn.mtianyan.sort;
public class CatTwo {
private String name; //名字
private int month; //年龄
private String species;//品种
@Override
public String toString() {
return "[姓名：" + name + ", 年龄：" + month + ", 品种：" + species + "]";
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getMonth() {
return month;
}
public void setMonth(int month) {
this.month = month;
}
public String getSpecies() {
return species;
}
public void setSpecies(String species) {
this.species = species;
}
public CatTwo(String name, int month, String species) {
this.name = name;
this.month = month;
this.species = species;
}
}
package cn.mtianyan.sort;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
public class CatTwoTest {
public static void main(String[] args) {
List<CatTwo> list = new ArrayList<>();
// 定义宠物猫对象
CatTwo huahua = new CatTwo("aa", 12, "英国短毛猫");
CatTwo fanfan = new CatTwo("bb", 3, "中华田园猫");
CatTwo huahua02 = new CatTwo("cc", 2, "英国短毛猫");
list.add(huahua);
list.add(fanfan);
list.add(huahua02);
System.out.println("排序前宠物猫信息");
for (CatTwo cat: list) {
System.out.println(cat);
}
Comparator<CatTwo> comparator = new Comparator<CatTwo>() {
@Override
public int compare(CatTwo o1, CatTwo o2) {
return o1.getMonth() - o2.getMonth();
}
};
Collections.sort(list,comparator);
System.out.println("排序后宠物猫信息(按月份从小到大)");
for (CatTwo cat: list) {
System.out.println(cat);
}
}
}
运行结果:
字符串名字从大到小
@Override
public int compare(CatTwo o1, CatTwo o2) {
// return o1.getMonth() - o2.getMonth();
return o2.getName().compareTo(o1.getName());
}
};
Collections.sort(list,comparator);
System.out.println("排序后宠物猫信息(按名字从大到小)");
运行结果:
package cn.mtianyan.sort;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
public class SortArray {
public static void main(String[] args) {
Character [] charArray = new Character[]{'m','t','i','a','n','y','a','n'};
List<Character> list = Arrays.asList(charArray);
System.out.println("====Character排序前====");
for (Character character:list) {
System.out.print(character+" ");
}
System.out.println();
System.out.println("====Character正序排序后====");
Collections.sort(list);
for (Character character:list) {
System.out.print(character+" ");
}
System.out.println();
System.out.println("====Character逆序排序后====");
Collections.sort(list,Collections.reverseOrder());
for (Character character:list) {
System.out.print(character+" ");
}
String [] stringArray = new String[]{"yes","ha","mtianyan","ab"};
System.out.println();
List<String> list1 = Arrays.asList(stringArray);
System.out.println("====String排序前====");
for (String string:list1) {
System.out.print(string+" ");
}
System.out.println();
Collections.sort(list1);
System.out.println("====String正序排序后====");
for (String string:list1) {
System.out.print(string+" ");
}
Comparator cmp1 = Collections.reverseOrder();
Collections.sort(list1,cmp1);
System.out.println();
System.out.println("====String逆序排序后====");
for (String string:list1) {
System.out.print(string+" ");
}
Integer[] intArray = new Integer[]{8,6,3,4,7,5,1};
List<Integer> list2 = Arrays.asList(intArray);
System.out.println();
System.out.println("====Integer排序前====");
for (Integer integer:list2) {
System.out.print(integer+" ");
}
System.out.println();
System.out.println("====Integer正序排序后====");
Collections.sort(list2);
for (Integer integer:list2) {
System.out.print(integer+" ");
}
System.out.println();
System.out.println("====Integer逆序排序后====");
Collections.sort(list2,Collections.reverseOrder());
for (Integer integer:list2) {
System.out.print(integer+" ");
}
}
}
运行结果:
package cn.mtianyan.sort;
import java.util.HashSet;
import java.util.Set;
import java.util.concurrent.ConcurrentSkipListSet;
public class SortedMap {
public static void main(String[] args) {
Set<String> set = new HashSet<>();
set.add("ccc");
set.add("ddd");
set.add("eee");
set.add("aaa");
set.add("bbb");
for (String string:set){
System.out.println(string);
}
System.out.println("=============");
ConcurrentSkipListSet<String> concurrentSkipListSet = new ConcurrentSkipListSet<>();
concurrentSkipListSet.add("ccc");
concurrentSkipListSet.add("ddd");
concurrentSkipListSet.add("eee");
concurrentSkipListSet.add("aaa");
concurrentSkipListSet.add("bbb");
for (String string:concurrentSkipListSet) {
System.out.println(string);
}
}
}
运行结果:
https://www.zhihu.com/question/28414001
SortedMap接口的实现类ConcurrentSkipListMap
下一节我们将学习泛型。
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