安卓进阶之享学架构师-动态数组

package com.mj;

@SuppressWarnings("unchecked")
public class ArrayList {
  /**
   * 元素的数量
   */
  private int size;
  /**
   * 所有的元素
   */
  private E[] elements;
  
  private static final int DEFAULT_CAPACITY = 10;
  private static final int ELEMENT_NOT_FOUND = -1;
  
  public ArrayList(int capaticy) {
      capaticy = (capaticy < DEFAULT_CAPACITY) ? DEFAULT_CAPACITY : capaticy;
      elements = (E[]) new Object[capaticy];
  }
  
  public ArrayList() {
      this(DEFAULT_CAPACITY);
  }
  
  /**
   * 清除所有元素
   */
  public void clear() {
      for (int i = 0; i < size; i++) {
          elements[i] = null;
      }
      size = 0;
  }

  /**
   * 元素的数量
   * @return
   */
  public int size() {
      return size;
  }

  /**
   * 是否为空
   * @return
   */
  public boolean isEmpty() {
       return size == 0;
  }

  /**
   * 是否包含某个元素
   * @param element
   * @return
   */
  public boolean contains(E element) {
      return indexOf(element) != ELEMENT_NOT_FOUND;
  }

  /**
   * 添加元素到尾部
   * @param element
   */
  public void add(E element) {
      add(size, element);
  }

  /**
   * 获取index位置的元素
   * @param index
   * @return
   */
  public E get(int index) {
      rangeCheck(index);
      return elements[index];
  }

  /**
   * 设置index位置的元素
   * @param index
   * @param element
   * @return 原来的元素ֵ
   */
  public E set(int index, E element) {
      rangeCheck(index);
      
      E old = elements[index];
      elements[index] = element;
      return old;
  }

  /**
   * 在index位置插入一个元素
   * @param index
   * @param element
   */
  public void add(int index, E element) {
      rangeCheckForAdd(index);
      
      ensureCapacity(size + 1);
      
      for (int i = size; i > index; i--) {
          elements[i] = elements[i - 1];
      }
      elements[index] = element;
      size++;
  }

  /**
   * 删除index位置的元素
   * @param index
   * @return
   */
  public E remove(int index) {
      rangeCheck(index);
      
      E old = elements[index];
      for (int i = index + 1; i < size; i++) {
          elements[i - 1] = elements[i];
      }
      elements[--size] = null;
      return old;
  }

  /**
   * 查看元素的索引
   * @param element
   * @return
   */
  public int indexOf(E element) {
      if (element == null) {  // 1
          for (int i = 0; i < size; i++) {
              if (elements[i] == null) return i; 
          }
      } else {
          for (int i = 0; i < size; i++) {
              if (element.equals(elements[i])) return i; // n
          }
      }
      return ELEMENT_NOT_FOUND;
  }
  
//  public int indexOf2(E element) {
//      for (int i = 0; i < size; i++) {
//          if (valEquals(element, elements[i])) return i; // 2n
//      }
//      return ELEMENT_NOT_FOUND;
//  }
//  
//  private boolean valEquals(Object v1, Object v2) {
//      return v1 == null ? v2 == null : v1.equals(v2);
//  }
  
  /**
   * 保证要有capacity的容量
   * @param capacity
   */
  private void ensureCapacity(int capacity) {
      int oldCapacity = elements.length;
      if (oldCapacity >= capacity) return;
      
      // 新容量为旧容量的1.5倍
      int newCapacity = oldCapacity + (oldCapacity >> 1);
      E[] newElements = (E[]) new Object[newCapacity];
      for (int i = 0; i < size; i++) {
          newElements[i] = elements[i];
      }
      elements = newElements;
      
      System.out.println(oldCapacity + "扩容为" + newCapacity);
  }
  
  private void outOfBounds(int index) {
      throw new IndexOutOfBoundsException("Index:" + index + ", Size:" + size);
  }
  
  private void rangeCheck(int index) {
      if (index < 0 || index >= size) {
          outOfBounds(index);
      }
  }
  
  private void rangeCheckForAdd(int index) {
      if (index < 0 || index > size) {
          outOfBounds(index);
      }
  }
  
  @Override
  public String toString() {
      // size=3, [99, 88, 77]
      StringBuilder string = new StringBuilder();
      string.append("size=").append(size).append(", [");
      for (int i = 0; i < size; i++) {
          if (i != 0) {
              string.append(", ");
          }
          
          string.append(elements[i]);
          
//          if (i != size - 1) {
//              string.append(", ");
//          }
      }
      string.append("]");
      return string.toString();
  }
}