特点:存储和取出顺序不一样,无索引,不可重复
package com.zhongxin.day08; import java.util.HashSet; public class HashSetDemo { public static void main(String[] args) { HashSet<String> set = new HashSet<>(); set.add("测试"); set.add("测试"); set.add("a"); set.add("b"); set.add("c"); set.add("1"); set.add("2"); set.add("3"); System.out.println(set); // [a, 1, b, 2, c, 3, 测试] } }
System.out.println(set);
for (String e : set) { System.out.println(e); }
Iterator<String> it = set.iterator(); while (it.hasNext()) { String s = it.next(); System.out.println(s); }
import java.util.HashMap; HashMap<String, Integer> map = new HashMap<>();
package com.zhongxin.day08; import java.util.HashMap; public class HashMapDemo { public static void main(String[] args) { HashMap<String, Integer> map = new HashMap<>(); map.put("id", 100); map.put("age", 18); map.put("score", 60); System.out.println(map);//{score=60, id=100, age=18} map.put("score", 80); System.out.println(map);//{score=80, id=100, age=18} } }
int id = map.get("id"); System.out.println(id);//100 System.out.println(map.get("id1"));//null
System.out.println(map.size());//3
map.remove("id"); System.out.println(map);// {score=80, age=18}
import java.util.Set; Set<String> set = map.keySet(); System.out.println(set);// [score, age]
import java.util.Collection; Collection<Integer> values = map.values(); System.out.println(values);//[80, 18]
System.out.println(map.containsKey("score"));// true
Set<String> set_key = map.keySet(); for (String key : set_key) { int value = map.get(key); System.out.println(key + "=" + value); } //score=80 //age=18
Set<Map.Entry<String, Integer>> entrySet = map.entrySet(); for (Map.Entry<String, Integer> entry : entrySet) { System.out.println(entry.getKey() + "=" + entry.getValue()); }