Java 动态数组学习记录

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package array;   /**  * @date 2018/9/12  */ public class Array<E> {     private E[] data;     /**      * 存入的数据数量      */     private int size;       // 构造函数，传入数组的容量capacity构造Array     public Array(int capacity) {         data = (E[]) new Object[capacity];         size = 0;     }       // 无参数的构造函数，默认数组的容量capacity=10     public Array() {         this(10);     }       // 获取数组的容量     public int getCapacity() {         return data.length;     }       // 获取数组中的元素个数     public int getSize() {         return size;     }       // 返回数组是否为空     public boolean isEmpty() {         return size == 0;     }       // 在index索引的位置插入一个新元素e     public void add(int index, E e) {         if (index < 0 || index > size)             throw new IllegalArgumentException("获取失败,索引越界");         // 自动扩容 resize()         if (size == getCapacity()) {             resize(getCapacity() * 2);         }         // 插入之后元素后移         for (int i = size - 1; i >= index; i--) {             data[i + 1] = data[i];         }         data[index] = e;         size++;     }       // 向所有元素后添加一个新元素     public void addLast(E e) {         add(size, e);     }       // 在所有元素前添加一个新元素     public void addFirst(E e) {         add(0, e);     }       // 获取index索引位置的元素     public E get(int index) {         if (index < 0 || index >= size)             throw new IllegalArgumentException("获取失败,索引越界");         return data[index];     }       // 获取末尾元素     public E getLast() {         return data[size - 1];     }       // 获取头元素     public E getFirst() {         return data[0];     }       // 修改index索引位置的元素为e     public void set(int index, E e) {         if (index < 0 || index >= size)             throw new IllegalArgumentException("获取失败,索引越界");         data[index] = e;     }       // 查找数组中是否有元素e     public boolean contains(E e) {         for (int i = 0; i < size; i++) {             if (data[i].equals(e))                 return true;         }         return false;     }       // 查找数组中元素e所在的索引，如果不存在元素e，则返回-1     public int find(E e) {         for (int i = 0; i < size; i++) {             if (data[i].equals(e))                 return i;         }         return -1;     }       // 从数组中删除index位置的元素, 返回删除的元素     public E remove(int index) {         if (index < 0 || index >= size)             throw new IllegalArgumentException("获取失败,索引越界");         E ret = data[index];         for (int i = index+1; i < size; i++) {             data[i-1] = data[i];         }         size--;         data[size] = null;         // resize()         if (size == getCapacity() / 4 && getCapacity() / 2 != 0) {             resize(getCapacity() / 2);         }         return ret;     }       // 从数组中删除第一个元素, 返回删除的元素     public E removeFirst() {         return remove(0);     }       // 从数组中删除最后一个元素, 返回删除的元素     public E removeLast() {         return remove(size - 1);     }       // 从数组中删除元素e     public void removeElement(E e) {         int index = find(e);         if (index != -1) {             remove(index);         }     }       // tostring     @Override     public String toString() {         StringBuilder res = new StringBuilder();         res.append(String.format("array.Array: size=%d , capacity=%d\n", size, data.length));         res.append('[');         for (int i = 0; i < size; i++) {             res.append(data[i]);             if (i != size - 1)                 res.append(',');         }         res.append(']');         return res.toString();     }       // 将数组空间的容量变成newCapacity大小     public void resize(int newCapacity) {         E[] newData = (E[]) new Object[newCapacity];         for (int i = 0; i < size; i++) {             newData[i] = data[i];         }         data = newData;     }     public static void main(String[] args) {         Array<Integer> array = new Array<>();         for (int i = 0; i < 10; i++) {             array.addLast(i);         }         System.out.println(array);           array.removeLast();         System.out.println(array);         array.remove(0);         System.out.println(array);         array.removeLast();         System.out.println(array);         array.remove(0);         System.out.println(array);         array.removeLast();         System.out.println(array);         array.remove(0);         System.out.println(array);         array.removeLast();         System.out.println(array);         array.remove(0);         System.out.println(array);     } }