【自定义】 ArrayList

约定不等于承诺〃 2022-04-23 14:24 162阅读 0赞

## 自定义ArrayList ##

/** * 定义一个数组列表，需要有哪些方法和参数 * @ClassName: MyArrayList */
    public class MyArrayList<E> implements Serializable
    { 
    
        private static final long serialVersionUID = -5179259308804963168L;
        
        // 数组长度
        private int size;
        /** 默认初始化容量 */
        private static final int DEFAULT_CAPACITY = 10;
        // 数据对象
        private Object elementData [];
        
        private static Object [] EMPTY_ELEMENTDATA = { };
        
        public MyArrayList()
        { 
            elementData = EMPTY_ELEMENTDATA;
        }
        public MyArrayList(int size)
        { 
            if (size < 0) { 
                throw new IllegalArgumentException("Illegal Argument "+size);
            }
            
            elementData = new Object[size];
        }
        
        
        /** * add 方法 * @param */
        public boolean add(Object obj) { 
            // 确认数组的容量
            ensureCapacityInternal(size + 1);
            elementData[size++] = obj;
            return true;
        }
        
        public int size() { 
            return size;
        }
        
        private void ensureCapacityInternal(int minCapacity)
        { 
            // 判断数组是否为空
            if (elementData == EMPTY_ELEMENTDATA) { 
                minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);
            }
            
            if (elementData.length < minCapacity) { 
                elementData = Arrays.copyOf(elementData, minCapacity);
            }
        }
        /** * add 方法 * @param */
        public E get(int index) { 
            if (index > elementData.length - 1 || index < 0) { 
                throw new IllegalArgumentException("Illegal Argument "+index);
            }
            
            return elementData(index);
        }
        
        @SuppressWarnings("unchecked")
        E elementData(int index) { 
            return (E) elementData[index];
        }
        
        
        public E remove(int index) { 
            
            if (index >= elementData.length) { 
                throw new IndexOutOfBoundsException();
            }
            
            E oldValue = elementData(index);
            int numMoved = size - index - 1;
            
            if (numMoved > 0)
                System.arraycopy(elementData, index+1, elementData, index,
                                 numMoved);
            elementData[--size] = null; // clear to let GC do its work
            
            
            
            return oldValue;
        }
        
        // toString方法
        public String toString()
        { 
            if (this.size == 0) { 
                return "[]";
            } else { 
              StringBuffer st = new StringBuffer("[");
              for (int i =0 ;i< this.size;i++) { 
                  if (i== size-1) { 
                      st.append(elementData[i]).append("]");
                  }else { 
                      st.append(elementData[i]).append(",");
                  }
              }  
              
              return String.valueOf(st);
            }
            
        }
    
    }