数据类型

变量类型决定占据内存空间的大小。

数组

//数据遍历
public static void main(String[] args) {
    int[] arr = new int[4];
    arr[0] = 15;
    arr[1] = 98;
    for (int num:arr){
        System.out.println(num);
    }
}
//15 98 0 0

集合（容器）

Collection

• List

• CopyOnWriteArrayList

• Vector、Stack

• ArrayList

• LinkedList

• Set

• HashSet、LinkedHashSet

• SortedSet、TreeSet
• EnumSet
• CopyOnWriteArraySet
• ConcurrentSkipListSet

• Queue

• Deque

  • ArrayDeque

  • BlockingDeque、LinkedBlockingDeque

• BlockingQueue

  • ArrayBlockingQueue

  • PriorityBlockingQueue

  • LinkedBlockingQueue

  • TransferQueue、LinkedTransferQueue

  • SynchronousQueue

  • DelayQueue

• PriorityQueue

• ConcurrentLinkedQueue

Map

• HashMap、LinkedHashMap
• TreeMap
• WeakHashMap
• IdentityHashMap
• ConcurrentHashMap
• ConcurrentSkipListMap

public static void main(String[] args) {
    //定义一个集合
    ArrayList list = new ArrayList();
    System.out.println(list);
    //add
    list.add("aaa");
    list.add("bbb");
    list.add("ccc");
    list.add("ddd");
    System.out.println(list);
    //删
    list.remove("bbb");
    System.out.println(list);
    //改
    list.set(0, "eee");
    System.out.println(list);
    //查看
    System.out.println(list.get(2));
    //遍历
    for (int i = 0; i <= list.size() - 1; i++) {
        System.out.println(list.get(i));
    }
}