Treemap的基本用法

TreeMap：通过树结构来实现Map接口的。

TreeMap保证了映射按照升序顺序排列key

支持快速查找

键值对 key，value

key的值

由于TreeMap会对key进行排序，所有i我们必须保证所传的key是能够排序的。

如何把普通的类变成可排序的类？

实现Comparable接口，重写 compareTo（Object obj）方法

class Teacher implements Comparable {
    private int age;
    private String name;

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = 10;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public int compareTo(Object arg0) {
        // TODO Auto-generated method stub
        if (!(arg0 instanceof Teacher)) {
            return 1;
        }
        Teacher t1 = (Teacher) arg0;

        return this.age - t1.getAge();
    }

}

public class MapTest extends Teacher {

    public static void main(String[] args) {
        TreeMap tm = new TreeMap();
        tm.put(0, "zero");
        tm.put(1, "one");
        tm.put(3, "three");
        tm.put(2, "two");
        // System.out.println(tm);// {0=zero, 1=one, 2=two, 3=three}
        // System.out.println(tm.keySet());// [0, 1, 2, 3]
        // System.out.println(tm.values());// [zero, one, two, three]

        Set keys = tm.keySet();// set本身就是一个集合
        for (Integer key : keys) {
            System.out.print("学号：" + key + ",姓名：" + tm.get(key) + "\t");
        }

    }