【集合（容器）】ArrayList基础

查询效率高，增删效率低，线程不安全

建立包ArrayList

TestArrayList

public class TestArrayList  {
    
    

    private  Object[] elementData;
    private  int size;

    private  static final int DEFALT_CAPACITY=10;

    public  TestArrayList(){
    
    
        elementData=new Object[DEFALT_CAPACITY];
    }

    public TestArrayList(int capacity){
    
    
        elementData=new Object[capacity];
    }

    public void add(Object obj){
    
    
        elementData[size++]=obj;
    }

    //重写toString方法
    @Override
    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,']');//将逗号替换为]
        return sb.toString();
    }

    public static void main(String[] args) {
    
    

        TestArrayList s1=new TestArrayList(20);
        s1.add("aa");
        s1.add("bb");

        System.out.println(s1);
    }
}

TestArrayList02(数组扩容)

/*
数组扩容
 */
public class TestArrayList02<E>  {
    
    

    private  Object[] elementData;
    private  int size;

    private  static final int DEFALT_CAPACITY=10;

    public  TestArrayList02(){
    
    
        elementData=new Object[DEFALT_CAPACITY];
    }

    public TestArrayList02(int capacity){
    
    
        elementData=new Object[capacity];
    }

    public void add(E e){
    
    
        if(size==elementData.length){
    
    //扩容操作

            Object[] newArray=new Object[elementData.length+(elementData.length>>1)];//10->10+10/2

            System.arraycopy(elementData,0,newArray,0,elementData.length);

            elementData=newArray;
        }

        elementData[size++]=e;
    }

    @Override
    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,']');//将逗号替换为]
        return sb.toString();
    }

    public static void main(String[] args) {
    
    

        TestArrayList02 s1=new TestArrayList02();
        for(int i=0;i<20;i++){
    
    
            s1.add("若颂"+i);
        }

        System.out.println(s1);
    }
}

TestArrayList03（set和get方法数组边界检查）

public class TestArrayList03<E> {
    
    
    private  Object[] elementData;
    private  int size;

    private  static final int DEFALT_CAPACITY=10;

    public  TestArrayList03(){
    
    
        elementData=new Object[DEFALT_CAPACITY];
    }

    public TestArrayList03(int capacity){
    
    
        if(capacity<0){
    
    
            throw new RuntimeException("容器容量不能为负数！");
        }else if(capacity==0){
    
    
            elementData=new Object[DEFALT_CAPACITY];
        }else {
    
    
            elementData = new Object[capacity];
        }
    }

    public void add(E e){
    
    
        if(size==elementData.length){
    
    //实现扩容

            Object[] newArray=new Object[elementData.length+(elementData.length<<1)];//10->10+10/2

            System.arraycopy(elementData,0,newArray,0,elementData.length);

            elementData=newArray;
        }

        elementData[size++]=e;
    }

    //获取
    public E get(int index){
    
    
        checkRange(index);
        return (E)elementData[index];
    }

    //修改指定位置
    public void set(E element,int index){
    
    
        checkRange(index);
        elementData[index]=element;
    }

    public void checkRange(int index){
    
    
        //索引合法判断，[0，size)  10  0~9
        if(index<0||index>size-1){
    
    
            //不合法
            throw new RuntimeException("索引不合法："+index);
        }
    }

    @Override
    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,']');//将逗号替换为]
        return sb.toString();
    }

    public static void main(String[] args) {
    
    

        TestArrayList03 s1=new TestArrayList03();
        for(int i=0;i<20;i++){
    
    
            s1.add("suo"+i);
        }

        s1.set("ddd",10);
        System.out.println(s1);
        System.out.println(s1.get(19));
    }

}

TestArrayList04（remove删除操作）

public class TestArrayList04<E> {
    
    

    private  Object[] elementData;
    private  int size;

    private  static final int DEFALT_CAPACITY=10;

    public  TestArrayList04(){
    
    
        elementData=new Object[DEFALT_CAPACITY];
    }

    public TestArrayList04(int capacity){
    
    
        elementData=new Object[capacity];
    }

    public int size(){
    
      //返回私有size
        return size;
    }

    public boolean isEmpty(){
    
       //查看size是否为空
        return size==0?true:false;
    }

    public void add(E e){
    
    
        if(size==elementData.length){
    
    //实现扩容

            Object[] newArray=new Object[elementData.length+(elementData.length<<1)];//10->10+10/2

            System.arraycopy(elementData,0,newArray,0,elementData.length);

            elementData=newArray;
        }

        elementData[size++]=e;
    }

    public E get(int index){
    
    

        checkRange(index);
        return (E)elementData[index];
    }

    public void set(E element,int index){
    
    

        checkRange(index);
        elementData[index]=element;

    }

    public void checkRange(int index){
    
    
        //索引合法判断，[0，size)  10  0~9
        if(index<0||index>size-1){
    
    
            //不合法
            throw new RuntimeException("索引不合法："+index);
        }
    }

    public void remove(E element){
    
    
        //element将它和所有元素挨个比较，获得第一个比较为true的，返回
        for(int i=0;i<size;i++){
    
    
            if(element.equals(get(i))){
    
    //容器中所有比较操作都是用equals而不是==
                //将该元素从此处移除
                remove(i);
            }
        }
    }

    public void remove(int index){
    
    
        //移除指定位置元素
        int numMoved=elementData.length-index-1;
        if(numMoved>0){
    
    
            System.arraycopy(elementData,index+1,elementData,index,numMoved);
        }

        elementData[--size]=null;
    }

    @Override
    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,']');//将逗号替换为]
        return sb.toString();
    }

    public static void main(String[] args) {
    
    

        TestArrayList04 s1=new TestArrayList04();
        for(int i=0;i<40;i++){
    
    
            s1.add("suo"+i);
        }
        s1.set("dddd",10);
        System.out.println(s1);
        System.out.println(s1.get(39));

        s1.remove(3);
        s1.remove("suo11");
        System.out.println(s1);
        System.out.println(s1.size);
        System.out.println(s1.isEmpty());
    }
}