j2ee_01_ Collections Framework 01

Collections Framework 01

1. Collection Interface
   top-level interface 1.1 Collections Framework
   1.2 is the parent Set List interface and
   the interface is not a parent but 1.3 Map of
   the collection can only add a reference to the type of data (automatic boxing and unboxing after jdk1.5)

2. List Interface

  		List li = new ArrayList();
    		li.add("hh");
    		li.add("dd");
    		li.add("ww");

2.1 Features: orderly, objects can be repeated

		//1)有序  数据存入顺序与输出顺序一致
		for (Object it : li) {
			System.out.println(it);
		}
		
		System.out.println("---------------------------");
		//2)不唯一  可以出现重复数据
		li.add("mmd");
		for (Object it : li) {
			System.out.println(it);
		}

2.2 traversal
2.2.1 subscript
2.2.2 foreach (> = jdk1.5)

	for (Object it : li) {
			System.out.println(it);
		}

2.2.3 迭代器Iterator（原理）

	System.out.println("--------------iterator--------------");
		Iterator it = li.iterator();
		while(it.hasNext()) {
			System.out.println(it.next());
		}

2.3 List optimize
the initial capacity of 10,
a load factor of 0.5 (expansion ratio) 0.5
Capacity formula: container size 10 * 0.5 +
2.4 List element deletion

		System.out.println("第一种");

 		 for (int i = 0; i <li.size() ; i++) {
			li.remove(0);
		}
		System.out.println("第二种倒叙删除");
		for (int i = li.size()-1; i>=0; i--) {
			li.remove(i);
		}

3. Generic
   After JDK1.5
   to class type as a parameter called generic
   role: to improve the robustness of the program, to simplify the code
   default value of generic Object

4. Packing, unboxing
   a value type -> reference type boxed
   > unboxing a value type - reference type
   is introduced so automatic packing and unpacking function after jdk1.5

		//1)装箱,值类型-->引用类型
		int a = 4;
		Integer b = new Integer(a);
		//2)拆箱,应用类型-->值类型
		Integer c = new Integer(3);
		int d =c.intValue();

5. ArrayList, LinkedList, Vector difference
   ArrayList: a continuous array of structures for storing data, query block (subscript), additions and deletions slow
   LinkedList: structural stored data list, query slow, additions and deletions fast
   Vector: CRUD are slow, has old-fashioned

General flow chart of a set of frame