Detailed explanation of java list usage examples-javaTutorial-php.cn

Detailed explanation of java list usage examples

高洛峰

Release： 2017-01-22 15:42:08

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|--List: The elements are in order (you can take them out how you save them, the order will not be messed up), and the elements can be repeated (there can be a 3 on subscript 1, and there can also be a 3 on subscript 2) Because the collection system has an index,
|-- ArrayList: The underlying data structure uses an array structure (the array length is variable and can be extended by 50%) (the characteristic is that the query is fast, but additions and deletions are slow) Threads are out of sync
|-- LinkedList: The underlying data structure is a linked list structure (characterized by slow query and fast addition and deletion)
|-- Vector: The underlying data structure is an array data structure and thread synchronization (the array length is variable 100% extension) (both query and addition and deletion are very slow, replaced by ArrayList)

List: unique method, any method that can operate the subscript is unique to the system

Add

boolean add(int index, E element)
boolean addAll(index,Collection)

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 public static void List_add(){
     ArrayList a1 = new ArrayList();
     a1.add("java");
     a1.add("php");//List集合中的元素可以重复
    a1.add(".net");
     System.out.println("原集合："+a1);
     a1.add(1, "Flash");
     a1.add(0, "ps");    
     System.out.println(a1);

    ArrayList a2 = new ArrayList();
    a2.add("javascript");
    a2.add("3dMax");
    a2.add("IBM");

    a1.addAll(0, a2);
    System.out.println(a1);
}

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Delete the element at the specified position

 boolean remove(int index)

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 public static void List_remove(){
     ArrayList a1 = new ArrayList();
     a1.add("javascript");
     a1.add("php");
     a1.add("flash");
     System.out.println("原集合："+a1);

     a1.remove(0);
     System.out.println(a1);
}

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Modify the element with the specified index set(int index, E element) Returns the modified element

 public static void List_set() {
     ArrayList a1 = new ArrayList();
     a1.add("javascript");
     a1.add("php");
     a1.add(".net");
     System.out.println("原集合："+a1);

     a1.set(1, "falsh");
     System.out.println(a1);
}

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Check

get(int index)   返回列表中指定位置的元素
subList(int fromIndex, int toIndex)    
返回列表中指定的 fromIndex（包括 ）和 toIndex（不包括）之间的部分元素。

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 public static void List_get() {
     ArrayList a1 = new ArrayList();
     a1.add("java");
     a1.add("php");
     a1.add("flash");

     System.out.println(a1.get(0));//获取指定角标的元素，有了该方法就可以遍历该集合中的所有元素

     System.out.println(a1.subList(1, 3));//获取集合中某一部分的元素,包含头不包含尾
}

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Iterator unique to the List collection: ListIterator (a sub-interface of Iterator)

Note:
During iteration, the collection cannot be manipulated through the methods of the collection object. Elements in
Because a ConcurrentModificationException exception (concurrency exception) will occur
So, in the iterator, you can only use the iterator method to create elements
Because the Iterator method is limited, you can only judge the elements , take out, delete operations
If you want other operations such as adding, modifying, etc., you need to use its sub-interface, ListIterator
This interface can only be obtained through the listIterator method of the List collection

 public class ListIteratorDemo {
     public static void main(String[] args) {
         ArrayList a1 = new ArrayList();
         a1.add("java01");
         a1.add("java02");
         a1.add("java03");
         a1.add("java04");

         System.out.println("原集合是："+a1);

      /*在迭代过程中准备添加或者删除元素
      Iterator it = al.iterator();
      while (it.hasNext()){
      　　Object obj = it.next();

      　　if (obj.equals("java02"))
      　　//al.add("java008");//会出现并发异常，因为迭代器正在操作集合，不能再用集合的方法操作集合了
      　　it.remove();//将java02的引用从集合中删除了
      　　System.out.println("obj:"+obj);
        }
        */   
    //只有List的listIterator有增，删，改，查这些功能，因为只有List有索引
       ListIterator li = a1.listIterator();
          while (li.hasNext()){
          if(li.next().equals("java02"))
          //li.add("java009");
          li.set("java006");
        }   
    }
}

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Vector: Enumeration is a unique extraction method of Vector, which is very similar to iterator (in fact, enumeration and iteration are the same) and has been replaced by iterator

 public class VectorDemo {
     public static void main(String[] args) {
         Vector v = new Vector();
         v.add("java01");
         v.add("java02");
         v.add("java03");
         v.add("java04");

         for(Enumeration en = v.elements();en.hasMoreElements();){
            System.out.println(en.nextElement());
        }
    }
}

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LinkedList:

Special method:

addFirst();Add elements at the head addLast();Add elements at the tail

getFirst(); getLast(); Get elements but do not delete elements. If there are no elements in the collection, NoSuchElementException will occur

removeFirst(); removeLast(); gets the element but deletes the element. If there are no elements in the collection, NoSuchElementException will occur

In JDK1.6, alternative methods

offerFirst(); offerLast();

peekFirst(); peekLast() ; Get the element, but the element is not deleted. If there are no elements in the collection, null will be returned

pollFirst(); pollLast(); The element is obtained, but the element is deleted. If there are no elements in the collection, null will be returned

public class LinkedListDemo {
     public static void main(String[] args) {
         LinkedList link = new LinkedList();
         link.add("java01");
         link.add("java02");
         link.add("java03");
         link.add("java04");

         while(!link.isEmpty()){
            System.out.println((link.removeLast()));
        }
    }
}

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