Container-LinkedList to obtain the source code analysis of elements (10)

Container-LinkedList to obtain the source code analysis of elements (10)

1. LinkedList get elements

    //获取元素
           for (int i=0;i<list.size();i++){
         
         
               System.out.println(list.get(i));
           }
   

2. The method to actually get the element is list.get(i);

   • Ctrl+left mouse button and click get,

         E get(int index);
     

   • Use Ctrl+Alt to select the LinkedList interface implementation class of the get method

     /**
          * Returns the element at the specified position in this list.
          *
          * @param index index of the element to return
          * @return the element at the specified position in this list
          * @throws IndexOutOfBoundsException {@inheritDoc}
          */
         public E get(int index) {
             
             //根据索引的位置返回元素的方法
             checkElementIndex(index);//校验index是否合法
             return node(index).item;
         }
     
     

   • We look at the checkElementIndex method

      private void checkElementIndex(int index) {
             
             
             if (!isElementIndex(index))
                 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
         }
     

   • Look at the isElementIndex(index) method again

         /**
          * Tells if the argument is the index of an existing element.
          */
         private boolean isElementIndex(int index) {
             
             
             return index >= 0 && index < size;//这里跟之前的那个不同，索引要大于等于0，索引小于元素的个数，不能取等于，因为元素的个数时从1开始的，长度要比索引小一位的
         }
     

   • Then go back and look at the method of the checkElementIndex method

      private void checkElementIndex(int index) {
             
             
             if (!isElementIndex(index))
                 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
              //如果isPositionIndex返回的是true,再取非，则不执行if条件语句,证明索引没问题
             //如果isPositionIndex返回的是false,再取非，则执行if条件语句，抛出异常
         }
     
     

   • Then look back at the get(int index) method

         public E get(int index) {
             
             //根据索引的位置返回元素的方法
             checkElementIndex(index);//校验index是否合法//这个已经执行完
             return node(index).item;//然后通过node方法完之后，又去调用item这个存放元素的成员变量，这个方法返回的是 E，所以把成员变量的值返回回去了
         }
     
     

   • Or the node method we just analyzed

     /**
          * Returns the (non-null) Node at the specified element index.
          */
         Node<E> node(int index) {
             
             
             // assert isElementIndex(index);
     
             if (index < (size >> 1)) {
             
             
                 Node<E> x = first;
                 for (int i = 0; i < index; i++)
                     x = x.next;
                 return x;
             } else {
             
             
                 Node<E> x = last;
                 for (int i = size - 1; i > index; i--)
                     x = x.prev;
                 return x;
             }
         }
     

   • Schematic diagram of node:

• Then look at the get method, 33 is returned, and then 33.item, so that the element with address 33 is retrieved

  
  ​```java
      public E get(int index) {
        
        //根据索引的位置返回元素的方法
          checkElementIndex(index);//校验index是否合法//这个已经执行完
          return node(index).item;//然后通过node方法完之后，又去调用item这个存放元素的成员变量，这个方法返回的是 E，所以把成员变量的值返回回去了
      }
  
  ​```
  
  
  

• 33.item, so the element with address 33 is fetched, and the index is 2, which is correct.