1.集合框架
2.例子
package com.ligy.studymvc; import org.junit.jupiter.api.Test; import org.springframework.boot.test.context.SpringBootTest; import java.util.*; @SpringBootTest class StudymvcApplicationTests { @Test void test3() { Set<String> set = new HashSet<>(); set.add("aa"); set.add("bb"); //增强for for (String s : set) { System.out.println("set:" + s); } } @Test void test2() { Map<String, Object> map = new HashMap<>(); //1.put get map.put("a", "aa"); System.out.println("a:" + map.get("a")); } @Test void test1() { //多态 Collection<String> collection = new ArrayList<>(); //1.tostring() System.out.println(collection); //2.add collection.add("aa"); collection.add("aa"); collection.add("bb"); collection.add("cc"); System.out.println(collection); //3.remove collection.remove("aa"); System.out.println(collection); //4.clear //collection.clear(); //System.out.println(collection); //5.isEmpty if (collection.isEmpty()) { System.out.println("空"); } else { System.out.println("非空"); } //6.contains if (collection.contains("bb")) { System.out.println("包含:bb"); } else { System.out.println("不包含:bb"); } //7.size() System.out.println("size:" + collection.size()); //8.get System.out.println("0:" + ((ArrayList<String>) collection).get(0)); //9.迭代器。一个个读取,直到最后1个, Iterator<String> iterator = collection.iterator(); while (iterator.hasNext()) { System.out.println(iterator.next()); } } }