手工实现ArrayList3(增加set,get以及索引越界检查)

手工实现ArrayList3(增加set,get以及索引越界检查)

public class SxtArrayList04 <E>{
	private Object[] elementData;
	private int size;
	public static final int DEFAULT_CAPACITY=10;
	public SxtArrayList04() {
		elementData = new Object[DEFAULT_CAPACITY];
	}
	public SxtArrayList04(int capacity) {
		elementData = new Object[capacity];
	}
	public void add(E element) {
		//什么时候扩容
		if(size==elementData.length) {
		//怎么扩容
			Object[] newED = new Object[elementData.length*2];//10*2
			System.arraycopy(elementData, 0, newED, 0, elementData.length);
			elementData=newED;
		}
		elementData[size++] = element;
	}
	public String toString() {
		StringBuilder sb= new StringBuilder();
		sb.append("[");
		for(int i=0;i<size;i++) {
			sb.append(elementData[i]+",");
		}
		sb.setCharAt(sb.length()-1, ']');
		return sb.toString();
	}
	public E get(int index) {
		Check(index);
		return (E)elementData[index];
	}
	public void set(int index,E element) {
		Check(index);
		elementData[index]=element;
	}
	public void Check(int index) {
		if(index<0||index>size-1) {
			throw new RuntimeException("索引不合法:"+index);
		}
	}
	public static void main(String[] args) {
		SxtArrayList04<String> a1=new SxtArrayList04<>();
		for(int i=0;i<20;i++) {
			a1.add("第"+i);
		}
		a1.set(5, "阿狸");
		System.out.println(a1);
		System.out.println(a1.get(2));
	}
}

效果
1.异常效果

		a1.set(50, "阿狸");

		System.out.println(a1.get(200));

2.执行正确效果

	public static void main(String[] args) {
		SxtArrayList04<String> a1=new SxtArrayList04<>();
		for(int i=0;i<20;i++) {
			a1.add("第"+i);
		}
		a1.set(5, "阿狸");
		System.out.println(a1);
		System.out.println(a1.get(2));
	}