TreeMap与Iterator

1. TreeSet或TreeMap里面定义的是引用类型的话，就必须实现Comparable接口

import java.util.*;
 
public class a {
    public static void main(String[] args) {
        Map<Integer, String> treemap = new TreeMap();
        treemap.put(1, "aa");
        treemap.put(2, "bb");
        treemap.put(3, "cc");
        for (Integer key : treemap.keySet()) {
            System.out.println(key + "-----" + treemap.get(key));
        }
        /*
            1-----aa
            2-----bb
            3-----cc
        */
 
        TreeSet<Emp2> ts = new TreeSet<>();
        ts.add(new Emp2(1, "zs", 12222));
        ts.add(new Emp2(2, "ls", 11));
        ts.add(new Emp2(3, "ww", 333));
        for (Emp2 e: ts) {
            System.out.println(e);
        }
        /*
            id=2, name=ls, salary=11.0
            id=3, name=ww, salary=333.0
            id=1, name=zs, salary=12222.0
        */
    }
}
class Emp2 implements Comparable<Emp2> {
    int id;
    String name;
    double salary;
 
    @Override
    public String toString() {
        return "id=" + id + ", name=" + name + ", salary=" + salary ;
    }
 
    public Emp2(int id, String name, double salary) {
        super();
        this.id = id;
        this.name = name;
        this.salary = salary;
    }
 
    @Override
    public int compareTo(Emp2 o) {
        if (this.salary > o.salary) {
            return 1;
        } else if (this.salary < o.salary) {
            return -1;
        } else {
            if (this.id > o.id) {
                return 1;
            } else if (this.id < o.id) {
                return -1;
            } else {
                return 0;
            }
        }
    }
}

2. Iterator遍历list,map,set

import java.util.*;
 
public class a {
    public static void main(String[] args) {
        // 关于list
        List<Integer> list = new ArrayList<>();
        list.add(1);
        list.add(90);
        list.add(88);
        Iterator<Integer> iter = list.iterator();
        for ( ; iter.hasNext(); ) {
            Integer value = iter.next();
            System.out.println(value);
        }
        System.out.println("----------");
 
        // 关于set
        Set<String> set = new HashSet<>();
        set.add("1223");
        set.add("2345");
        set.add("0000");
        Iterator<String> iter2 = set.iterator();
        for ( ; iter2.hasNext(); ) {
            String value = iter2.next();
            System.out.println(value);
        }
        System.out.println("----------");
 
        Map<Integer, String> map = new HashMap<>();
        map.put(100, "aa");
        map.put(200, "bb");
        map.put(300, "cc");
        System.out.println("map法一");
        Set<Map.Entry<Integer, String>> entries = map.entrySet();
        Iterator<Map.Entry<Integer, String>> iterator = entries.iterator();
        for ( ; iterator.hasNext(); ) {
            Map.Entry<Integer, String> temp = iterator.next();
            System.out.println(temp.getKey() + "---" + temp.getValue());
        }
        System.out.println("map法二");
        Set<Integer> integers = map.keySet();
        Iterator<Integer> iterator1 = integers.iterator();
        for ( ; iterator1.hasNext(); ) {
            Integer next = iterator1.next();
            System.out.println(next + "---" + map.get(next));
        }
    }
}