手工实现ArrayList

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手工实现ArrayList01_最简化的方式

    package cn.yishan.mycollection;

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/**
* 自定义实现一个ArrayList,体会底层原理
* @author yishan
*/
public class SxtArrayList01 {
    private Object[] elementData;
    private int size;

    private static final int DEFAULT_CAPACITY = 10;

    public SxtArrayList01(){
    elementData = new Object[DEFAULT_CAPACITY];
    }
    public SxtArrayList01(int capacity){
        elementData = new Object[capacity];
    }

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

    @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,']');
        return sb.toString();
    }

    public static void main(String[] args) {
        SxtArrayList01 s1 = new SxtArrayList01(20);
        s1.add("aa");
        s1.add("bb");
        System.out.println(s1);
    }
}

手工实现ArrayList02_增加泛型

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package cn.yishan.mycollection;

/**
* 自定义实现一个ArrayList,体会底层原理
* 增加泛型
* @author yishan
*/
public class SxtArrayList02<E> {
    private Object[] elementData;
    private int size;

    private static final int DEFAULT_CAPACITY = 10;

    public SxtArrayList02(){
    elementData = new Object[DEFAULT_CAPACITY];
    }
    public SxtArrayList02(int capacity){
        elementData = new Object[capacity];
    }

    public void add(E element){
        elementData[size++] = element;
    }

    @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,']');
        return sb.toString();
    }

    public static void main(String[] args) {
        SxtArrayList02 s1 = new SxtArrayList02(20);
        s1.add("aa");
        s1.add("bb");
        System.out.println(s1);
    }
}

手工实现ArrayList03_增加数组扩容

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package cn.yishan.mycollection;

/**
* 自定义实现一个ArrayList,体会底层原理
* 增加数组扩容
* @author yishan
*/
public class SxtArrayList03<E> {
    private Object[] elementData;
    private int size;

    private static final int DEFAULT_CAPACITY = 10;

    public SxtArrayList03(){
    elementData = new Object[DEFAULT_CAPACITY];
    }
    public SxtArrayList03(int capacity){
        elementData = new Object[capacity];
    }

    public void add(E element){
        //什么时候扩容？
        if (size == elementData.length){
            //扩容操作
            Object[] newArray = new Object[elementData.length + (elementData.length>>1)];//10 --> 10+5

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

            elementData = newArray;
        }
        elementData[size++] = element;
    }

    @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,']');
        return sb.toString();
    }

    public static void main(String[] args) {
        SxtArrayList03 s1 = new SxtArrayList03(20);

        for (int i=0;i<40;i++){
            s1.add("山"+i);
        }
        System.out.println(s1);
    }
}

手工实现ArrayList04_索引越界问题_set和get方法

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package cn.yishan.mycollection;

/**
* 自定义实现一个ArrayList,体会底层原理
* 增加set和get方法
* 增加数组边界的检查
* @author yishan
*/
public class SxtArrayList04<E> {
    private Object[] elementData;
    private int size;

    private static final int DEFAULT_CAPACITY = 10;

    public SxtArrayList04(){
        elementData = new Object[DEFAULT_CAPACITY];
    }
    public SxtArrayList04(int capacity){

        if (capacity<0){
            throw new RuntimeException("容器的容量不能为负数");
        }else if (capacity == 0){
            elementData = new Object[DEFAULT_CAPACITY];
        }else {
            elementData = new Object[capacity];
        }
    }

    public void add(E element){
        //什么时候扩容？
        if (size == elementData.length){
            //扩容操作
            Object[] newArray = new Object[elementData.length + (elementData.length>>1)];//10 --> 10+5

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

            elementData = newArray;
        }
        elementData[size++] = element;
    }

    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）
        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,']');
        return sb.toString();
    }

    public static void main(String[] args) {
        SxtArrayList04 s1 = new SxtArrayList04(20);

        for (int i=0;i<40;i++){
            s1.add("山"+i);
        }
        s1.set("hhh",10);

        System.out.println(s1);
        System.out.println(s1.get(39));
    }
}

手工实现ArrayList05_增加remove方法

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package cn.yishan.mycollection;

/**
* 自定义实现一个ArrayList,体会底层原理
* 增加remove方法
* @author yishan
*/
public class SxtArrayList05<E> {
    private Object[] elementData;
    private int size;

    private static final int DEFAULT_CAPACITY = 10;

    public SxtArrayList05(){
        elementData = new Object[DEFAULT_CAPACITY];
    }
    public SxtArrayList05(int capacity){

        if (capacity<0){
            throw new RuntimeException("容器的容量不能为负数");
        }else if (capacity == 0){
            elementData = new Object[DEFAULT_CAPACITY];
        }else {
            elementData = new Object[capacity];
        }
    }

    public int size(){
        return size;
    }

    public boolean isEmpty(){
        return size==0?true:false;
    }

    public void add(E element){
        //什么时候扩容？
        if (size == elementData.length){
            //扩容操作
            Object[] newArray = new Object[elementData.length + (elementData.length>>1)];//10 --> 10+5

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

            elementData = newArray;
        }
        elementData[size++] = element;
    }

    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）
        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))){//容器中所有的比较操作都是equals，不是==
                //将该元素从此处移除
                remove(i);
            }
        }

    }

    public void remove(int index){
        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,']');
        return sb.toString();
    }

    public static void main(String[] args) {
        SxtArrayList05 s1 = new SxtArrayList05(20);

        for (int i=0;i<40;i++){
            s1.add("山"+i);
        }
        s1.set("hhh",10);

        System.out.println(s1);
        System.out.println(s1.get(39));
        s1.remove(3);
        s1.remove("山2");
        System.out.println(s1);
        System.out.println(s1.size);
        System.out.println(s1.isEmpty());
    }
}
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