容器,集合
collection的一些方法
List list = new ArrayList(); //add 添加 list.add(1); list.add("你好"); list.add(true); System.out.println("list:" + list); //remove 删除:1.指定元素删除 2.按索引删除 3. list.remove(0); System.out.println(list); //contatins 查是否包含某个元素 System.out.println(list.contains("你好")); //size 获取元素个数 System.out.println(list.size()); //isEmpty 判断集合是否为空 System.out.println(list.isEmpty()); //clear 清空集合 list.clear(); System.out.println(list); //addAll 添加多个元素 List list1 = new ArrayList(); list1.add("红楼梦"); list1.add("三国演义"); list1.add("水浒传"); list.addAll(list1); System.out.println(list); //containsAll 查看多个元素是否存在 System.out.println(list.containsAll(list1)); //removeAll 删除多个元素 list.add("聊斋"); list.removeAll(list1); System.out.println(list);
第一种遍历:迭代器(快捷键 :itit)
Collection c = new ArrayList(); c.add(new Book("红楼梦","曹雪芹","男",40)); c.add(new Book("三国演义","罗贯中","男",50)); c.add(new Book("水浒传","施耐庵","男",60)); c.add(new Book("西游记","吴承恩","男",70)); c.add("javalk"); //1:通过对象获取迭代器 Iterator iterator = c.iterator(); //2:使用while循环 while (iterator.hasNext()){//判断是否还有数据 Object object = iterator.next();//返回下一个元素,返回值类型:Object System.out.println(object); } //while循环快捷键 itit //显示所有键的快捷键 ctrl + j // while (iterator.hasNext()) { // Object next = iterator.next(); // // } //3.当退出while循环后,这是iterator指向最后元素,如果执行next()方法会报异常 //4.如希望在次遍历,需要重置迭代器 iterator = c.iterator();
第二种遍历:增强for循环(快捷键:大写I)
Collection c = new ArrayList(); c.add(new Book("红楼梦","曹雪芹","男",40)); c.add(new Book("三国演义","罗贯中","男",50)); c.add(new Book("水浒传","施耐庵","男",60)); c.add(new Book("西游记","吴承恩","男",70)); c.add("javalk"); /** * 增强for循环;底层依然是迭代器 * 参数一:返回值类型; * 参数二:名称(随意起); * 参数三:遍历的对象 * */ for (Object book: c){ System.out.println(book); } //也可以在数组使用 int[] num = {1,2,6,7,3}; for (int n : num){ System.out.println(n); }
List的方法
特点:
1.有序(添加顺序和取出顺序一致),可重复
2.list中的每个元素都有所有(从0开始)
常用子实现类:
1.ArrayList
2.linkedList
3.Vetor