8. 基于自动化–Java集合
一、List:ArrayList
容器支持的数据类型:引用类型
容器特点:有序、可重复
//1.创建ArrayList对象 ArrayList<String> list = new ArrayList(); System.out.println(list.size()); //2.添加数据元素:add list.add("张三"); list.add("李四"); list.add("王五"); System.out.println(list.size()); //3.取出数据 System.out.println(list.get(0)); //4.移除元素 list.remove(0); list.remove("李四"); //5.获取集合大小 System.out.println(list.size()); //6.判断是否包含某个元素 System.out.println(list.contains("王五")); //7.判断集合是否为空 System.out.println(list.isEmpty()); //8.修改某个位置元素 System.out.println(list.set(0,"修改元素")); System.out.println(list); list.add("张三"); list.add("张三"); //9.循环读取元素 for (String s:list) { System.out.println(s); }
二、Map:HashMap
键值对的形式存储,支持引用数据类型
容器特点:以键值对的形式保存;不可以重复,重复时,后者键值对覆盖前者
//1.创建HashMap对象 HashMap<String,String> map = new HashMap<>(); System.out.println(map.size()); //2.添加数据元素:put map.put("name","张三"); map.put("age","18"); //3.取出数据 System.out.println(map.get("name")); System.out.println(map.get("age")); //4.移除元素 map.remove("name"); //5.获取集合大小 System.out.println(map.size()); //6.判断是否包含某个键或值 System.out.println(map.containsKey("name")); System.out.println(map.containsValue("张三")); //7.判断集合是否为空 System.out.println(map.isEmpty()); //8.循环读取元素 for (String key:map.keySet()) { System.out.println(key + "===" + map.get(key)); } for (String value:map.values()) { System.out.println(value); } //Entry代表一个key-value Set<Map.Entry<String,String>> entries = map.entrySet(); for (Map.Entry<String,String> entry:entries) { System.out.println("key:"+entry.getKey()+",value:"+entry.getValue()); }
三、Set:HashSet
容器支持的数据类型:引用类型
容器特点:无序、不可重复
//1.创建HashMap对象 HashMap<String,String> map = new HashMap<>(); System.out.println(map.size()); //2.添加数据元素:put map.put("name","张三"); map.put("age","18"); //3.取出数据 System.out.println(map.get("name")); System.out.println(map.get("age")); //4.移除元素 map.remove("name"); //5.获取集合大小 System.out.println(map.size()); //6.判断是否包含某个键或值 System.out.println(map.containsKey("name")); System.out.println(map.containsValue("张三")); //7.判断集合是否为空 System.out.println(map.isEmpty()); //8.循环读取元素 for (String key:map.keySet()) { System.out.println(key + "===" + map.get(key)); } for (String value:map.values()) { System.out.println(value); } //Entry代表一个key-value Set<Map.Entry<String,String>> entries = map.entrySet(); for (Map.Entry<String,String> entry:entries) { System.out.println("key:"+entry.getKey()+",value:"+entry.getValue()); }
四、Collection