利用TreeMap对map进行排序

Treemap是可以根据键对map进行排序的，注意：是根据键。

一般来讲，键可以使Integer或者是String，

但是也可以是对象，但是该对象的实现类必须实现Comparable<T>接口。

class mycompare implements Comparable<mycompare>{    private int age;    private String name;    public mycompare(int age, String name) {        this.age = age;        this.name = name;    }    @Override    public String toString() {        return "people{" +                "age=" + age +                ", name='" + name + '\'' +                '}';    }    public int getAge() {        return age;    }    public void setAge(int age) {        this.age = age;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    @Override    public int compareTo(mycompare o) {        return this.getAge()-o.getAge();    }}public class TreeMapAndSet {    public static void main(String []args){        Map<mycompare, Integer> map1 = new TreeMap<>();        map1.put(new mycompare(1,"first"),1);        map1.put(new mycompare(2,"second"),2);        map1.put(new mycompare(4,"fourth"),3);        map1.put(new mycompare(5,"fifth"),4);        map1.put(new mycompare(3,"third"),5);        for(Map.Entry<mycompare,Integer> entry :map1.entrySet()){            System.out.println("键："+entry.getKey()+"-----值："+entry.getValue());        }    }}

输出：键：people{age=1, name='first'}-----值：1
键：people{age=2, name='second'}-----值：2
键：people{age=3, name='third'}-----值：5
键：people{age=4, name='fourth'}-----值：3
键：people{age=5, name='fifth'}-----值：4

想想用这样的方法对值进行排序就很简单了，再来一个HashMap即可。

另外，如果mycompare没有实现Comparable接口，也可以这样子写：

class mycompare{    private int age;    private String name;    public mycompare(int age, String name) {        this.age = age;        this.name = name;    }    @Override    public String toString() {        return "people{" +                "age=" + age +                ", name='" + name + '\'' +                '}';    }    public int getAge() {        return age;    }    public void setAge(int age) {        this.age = age;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }}public class TreeMapAndSet {    public static void main(String []args){        TreeMap<mycompare, Integer> treeMap2 = new TreeMap<>(new Comparator<mycompare>(){            public int compare(mycompare o1, mycompare o2) {                return o1.getAge()-o2.getAge();            }        });        treeMap2.put(new mycompare(1,"first"),1);        treeMap2.put(new mycompare(2,"second"),2);        treeMap2.put(new mycompare(4,"fourth"),3);        treeMap2.put(new mycompare(5,"fifth"),4);        treeMap2.put(new mycompare(3,"third"),5);        for(Map.Entry<mycompare,Integer> entry :treeMap2.entrySet()){            System.out.println("键："+entry.getKey()+"-----值："+entry.getValue());        }        /*Map<mycompare, Integer> map1 = new TreeMap<>();        map1.put(new mycompare(1,"first"),1);        map1.put(new mycompare(2,"second"),2);        map1.put(new mycompare(4,"fourth"),3);        map1.put(new mycompare(5,"fifth"),4);        map1.put(new mycompare(3,"third"),5);        for(Map.Entry<mycompare,Integer> entry :map1.entrySet()){            System.out.println("键："+entry.getKey()+"-----值："+entry.getValue());        }*/    }}

输出一样。

另外来一个直接对值进行排序的方法,也是不用实现comparator的：

class mycompare {    private int age;    private String name;    public mycompare(int age, String name) {        this.age = age;        this.name = name;    }    @Override    public String toString() {        return "people{" +                "age=" + age +                ", name='" + name + '\'' +                '}';    }    public int getAge() {        return age;    }    public void setAge(int age) {        this.age = age;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }}public class TreeMapAndSet {    public static void main(String []args){        Map<Integer,mycompare> map = new TreeMap<>();        map.put(1,new mycompare(1,"fff"));        map.put(2,new mycompare(2,"fff"));        map.put(3,new mycompare(4,"fff"));        map.put(4,new mycompare(3,"fff"));        map.put(5,new mycompare(5,"fff"));        List<Map.Entry<Integer,mycompare>> list = new ArrayList<Map.Entry<Integer, mycompare>>(map.entrySet());        Collections.sort(list, new Comparator<Map.Entry<Integer, mycompare>>() {            @Override            public int compare(Map.Entry<Integer, mycompare> o1, Map.Entry<Integer, mycompare> o2) {                return o1.getValue().getAge()-o2.getValue().getAge();            }        });       /* for(int i=0;i<list.size();i++){            System.out.println("键："+list.get(i).getKey()+"  值："+list.get(i).getValue());        }*/        for(Map.Entry<Integer,mycompare> e:list){            System.out.println(e.getKey()+"----"+e.getValue());        }    }}

输出：1----people{age=1, name='fff'}
2----people{age=2, name='fff'}
4----people{age=3, name='fff'}
3----people{age=4, name='fff'}
5----people{age=5, name='fff'}