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
     
       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。

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
     
       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
      
        comparator = new Comparator
       
        () {            @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
     
       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
      
        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
       
         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
     
       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
      
        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:

SortedMap接口的实现类ConcurrentSkipListMap

下一节我们将学习泛型。