一、TreeSet中比较器：

　　1）Comparable：实体类实现Comparable接口，重写compareTo方法；

　　2）Comparator：写一个实现类实现Comparator接口，重写compare方法；创建TreeSet时候传入该实体类的对象；

　　3）匿名实现Comparator；

　　4）lambdo实现Comparator；

二、Comparable：

　　1、实体类：

 

public class Person implements Comparable {    private String name;    private int age;    Person(String name,int age){        this.name=name;        this.age=age;    }    public String getName(){        return name;    }    public int getAge(){        return age;    }    //实现Comparable接口，重写compareTo方法；    public int compareTo(Object obj){        if (!(obj instanceof Person)){            throw new RuntimeException("不是正确对象");        }        Person p=(Person)obj;        if (p.age>this.age)return -1;        if (p.age==this.age){            return this.name.compareTo(p.name);        };        return 1;    }}

 

　　2、测试类：

public class Test {    public static void main(String[] args) {        TreeSet ts = new TreeSet();        ts.add(new Person("zs0", 20));        ts.add(new Person("zs1", 20));        ts.add(new Person("zs1", 21));        ts.add(new Person("zs9", 19));        for (Iterator
     
       it = ts.iterator(); it.hasNext(); ) {            Person p = it.next();            System.out.println(p.getName()+"..."+p.getAge());        }    }}
     

三、Comparator：

　　1、实体类：

public class Student {    private String name;    private int age;    public Student(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;    }    @Override    public String toString() {        return "Student{" +                "name='" + name + '\'' +                ", age=" + age +                '}';    }}

　　2、comparator实现类：

 

public class ComparatorImpl implements Comparator {    @Override    public int compare(Object o1, Object o2) {        if (o1==o2)return 0;        if (!(o1 instanceof Student) || !(o2 instanceof Student)){            throw new RuntimeException("类型不对");        }        Student s1=(Student)o1;        Student s2=(Student)o2;        int num=s1.getName().compareTo(s2.getName());        if (num==0){            return new Integer(s1.getAge()).compareTo(new Integer(s2.getAge()));        }        return num;    }}

　　3、测试类：

public class Test {    public static void main(String[] args) {        TreeSet ts=new TreeSet(new ComparatorImpl());        ts.add(new Student("z1", 1));        ts.add(new Student("z3", 3));        ts.add(new Student("z2", 2));        ts.add(new Student("z3", 2));        ts.add(new Student("z3", 2));        Iterator it=ts.iterator();        while (it.hasNext()){            System.out.println(it.next().toString());        }    }}

四、comparator匿名实现：

 

public class Test2 {    public static void main(String[] args) {        TreeSet ts = new TreeSet(new Comparator() {            @Override            public int compare(Object o1, Object o2) {                if (o1 == o2) return 0;                if (!(o1 instanceof Student) || !(o2 instanceof Student)) {                    throw new RuntimeException("类型不对");                }                Student s1 = (Student) o1;                Student s2 = (Student) o2;                int num = s1.getName().compareTo(s2.getName());                if (num == 0) {                    return new Integer(s1.getAge()).compareTo(new Integer(s2.getAge()));                }                return num;            }        });        ts.add(new Student("z1", 1));        ts.add(new Student("z3", 3));        ts.add(new Student("z2", 2));        ts.add(new Student("z3", 2));        ts.add(new Student("z3", 2));        Iterator it = ts.iterator();        while (it.hasNext()) {            System.out.println(it.next().toString());        }    }}

五、lambda实现comparator：

　　//lambda需要jdk1.8；

public class Test3 {    public static void main(String[] args) {        TreeSet ts = new TreeSet((o1, o2)->{            if (o1 == o2) return 0;            if (!(o1 instanceof Student) || !(o2 instanceof Student)) {                throw new RuntimeException("类型不对");            }            Student s1 = (Student) o1;            Student s2 = (Student) o2;            int num = s1.getName().compareTo(s2.getName());            if (num == 0) {                return new Integer(s1.getAge()).compareTo(new Integer(s2.getAge()));            }            return num;        });        ts.add(new Student("z1", 1));        ts.add(new Student("z3", 3));        ts.add(new Student("z2", 2));        ts.add(new Student("z3", 2));        ts.add(new Student("z3", 2));        Iterator it = ts.iterator();        while (it.hasNext()) {            System.out.println(it.next().toString());        }    }}