标签：ted eth current yar cep 指定 index case 修改
ArrayList是一个动态数组，Array的复杂版本，它提供了动态的增加和减少元素，实现了ICollection和IList接口，灵活的设置数组的大小等好处，ArrayList不是线程安全的。
在实现MyArrayList前先实现MyList，MyAbstractList，他们的关系如下。
MyArrayList--->（继承于）MyAbstractList--->（实现）MyList接口--->（实现）java.lang.Iterable接口
MyList接口定义如下
public interface MyList<E> extends Iterable<E> { public void add(E e); public void add(int index, E e); public void clear(); public boolean contains(E e); public E get(int index); public int indexOf(E e); public boolean isEmpty(); public int lastIndexOf(E e); public boolean remove(E e); public E remove(int index); public E set(int index, E e); public int size(); }
MyAbstractList类定义如下
public abstract class MyAbstractList<E> implements MyList<E> { protected int size = 0; protected MyAbstractList() { } protected MyAbstractList(E[] objects) { for(int i = 0; i < objects.length; i++) { add(objects[i]); } } @Override public void add(E e) { add(size, e); } @Override public boolean isEmpty() { return size == 0; } @Override public int size() { return size; } @Override public boolean remove(E e) { if(indexOf(e) >= 0) { remove(indexOf(e)); return true; }else { return false; } } }
MyArrayList定义如下
import java.util.Iterator; public class MyArrayList<E> extends MyAbstractList<E> { public static final int INITIAL_CAPACITY = 16;//初始容量 private E[]data = (E[])(new Object[INITIAL_CAPACITY]);; public MyArrayList() { } public MyArrayList(int length) { if(length >= 0) { data = (E[])(new Object[length]); } } public MyArrayList(E[] objects) { for(int i = 0; i < objects.length; i++) { add(objects[i]); } } @Override public void add(int index, E e) { // TODO Auto-generated method stub ensureCapacity(); for(int i = size - 1; i >= index; i--) {//将data[index]和后面的元素往后移动一位 data[i + 1] = data[i]; } data[index] = e; size++; } //判断容量满时，新建一个容量为原来两倍+1的数组 private void ensureCapacity() { if(size >= data.length) { E[] newData = (E[])(new Object[size * 2 + 1]);//java源码扩容1.5倍＋1 System.arraycopy(data, 0, newData, 0, size); data = newData; } } @Override public void clear() { // TODO Auto-generated method stub data = (E[])(new Object[INITIAL_CAPACITY]); size = 0; } @Override public boolean contains(E e) { // TODO Auto-generated method stub for(int i = 0; i < size; i++) { if(e.equals(data[i])) { return true; } } return false; } @Override public E get(int index) { // TODO Auto-generated method stub checkIndex(index);//判断下标是否合法 return data[index]; } private void checkIndex(int index) { if(index < 0 || index >= size) { throw new IndexOutOfBoundsException("index " + index + " out of bounds"); } } @Override public int indexOf(E e) { // TODO Auto-generated method stub for(int i = 0; i < size; i++) { if(e.equals(data[i])) { return i; } } return -1; } @Override public int lastIndexOf(E e) { // TODO Auto-generated method stub for(int i = size - 1; i >= 0; i--) { if(e.equals(data[i])) { return i; } } return -1; } @Override public E remove(int index) { // TODO Auto-generated method stub checkIndex(index);//判断下标是否合法 E e = data[index];//获取删除对象的值 for(int i = index; i < size - 1; i++) {//将data[index]后面的元素往前移动一位 data[i] = data[i+1]; } data[size] = null;//删除最后的元素 size--; return e; } @Override public E set(int index, E e) { // TODO Auto-generated method stub checkIndex(index);//判断下标是否合法 E old = data[index]; data[index] = e; return old; } //重写java.lang.Object.toString方法，打印整个数组 @Override public String toString() { StringBuilder result = new StringBuilder("["); for(int i = 0; i < size; i++) { result.append(data[i]); if(i < size - 1) { result.append(","); } } return result + "]"; } //新建一个刚好等于size的数组，即将数组容量设为刚好足够存放的大小 public void trimToSize() { if(size != data.length) { E[] newData = (E[])(new Object[size]); System.arraycopy(data, 0, newData, 0, size); data = newData; } } @Override public Iterator<E> iterator() { // TODO Auto-generated method stub return new ArrayListIterator(); } private class ArrayListIterator implements Iterator<E> { private int current = 0; @Override public boolean hasNext() { // TODO Auto-generated method stub return (current < size); } @Override public E next() { // TODO Auto-generated method stub return data[current++]; } } }
测试代码如下
public class TestMyArrayList { public static void main(String[] args) { // TODO Auto-generated method stub // String[] ss = {"China","America","Germany","Canada","France","Germany"}; MyList<String> list = new MyArrayList<String>(); System.out.println("测试add(E e)方法和add(int index, E e)方法添加数据。"); list.add("America"); list.add(0,"China"); list.add("Canada"); list.add("France"); list.add(2,"Germany"); list.add("Germany"); System.out.println("通过toString()方法打印数组" + list.toString()); System.out.println("通过size()方法获取长度：" + list.size()); System.out.println("测试contains()方法：" + list.contains("France")); System.out.println("通过get()方法获取指定下标的值：" + list.get(1)); System.out.println("通过indexOf()方法获取指定值的下标：" + list.indexOf("Germany")); System.out.println("通过lastIndexOf()方法获取最后出现的指定值的下标：" + list.lastIndexOf("Germany")); System.out.println("通过下标删除指定值：" + list.remove(5)); System.out.println("删除后的数组：" + list.toString()); System.out.println("通过set()方法修改值：" + list.set(2, "Russia")); System.out.print("通过foreach遍历数组："); for(String s:list) { System.out.print(s.toUpperCase() + " "); } } }
测试结果
思考：为什么MyArrayList类中的ensureCapacity()扩容倍数是2 * x + 1而不是2 * x？
因为如果我们创建了一个长度为0的数组，如果扩容倍数是2 * x，那么这个数组就无法扩容了。
标签：ted eth current yar cep 指定 index case 修改
原文地址：https://www.cnblogs.com/zhanghongcan/p/9026733.html
