java容器--------手工实现ArraList_最简单方式

一、第一中实现方式
package cn.zxg.collection;

/**
 * 自定义实现ArraList,体会底层原理
 */

public class SxtArraList {
    private int size;
    private  Object[] elementData;
    private static final int DEFALT_CAPACITY=10;
    public SxtArraList(){
        elementData=new Object[DEFALT_CAPACITY];
    }

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

    }

    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) {
        SxtArraList s1=new SxtArraList(20);
        s1.add("a");
        s1.add("b");
        System.out.println(s1);
    }
}

第二、增加扩容

package cn.zxg.collection;

/**
 * 自定义实现ArraList,体会底层原理
 */

public class SxtArraList <E>{
    private int size;
    private  Object[] elementData;
    private static final int DEFALT_CAPACITY=10;
    public SxtArraList(){
        elementData=new Object[DEFALT_CAPACITY];
    }

    public SxtArraList(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,10+10/2,要把(elementData.length>>1) 因为+的优先级比>>1高
            Object[] newArray=new Object[elementData.length+(elementData.length>>1)];
            System.arraycopy(elementData,0,newArray,0,elementData.length);
            elementData=newArray;

        }
        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 static void main(String[] args) {
        SxtArraList s1=new SxtArraList(20);
        for(int i=0;i<40;i++){
            s1.add("小白");
        }
        System.out.println(s1);
    }
}

第三版、增加get和set方法、对索引合法判断

package cn.zxg.collection;

/**
 * 自定义实现ArraList,体会底层原理
 * 1、增加get和set方法
 * 2、
 */

public class SxtArraList <E>{
    private int size;
    private  Object[] elementData;
    private static final int DEFALT_CAPACITY=10;
    public SxtArraList(){
        elementData=new Object[DEFALT_CAPACITY];
    }

    public SxtArraList(int capacity){
        if(capacity<0){
            throw new RuntimeException("容器容量不能为负");
        }else if(capacity==0){
            elementData=new Object[DEFALT_CAPACITY];
        }
        else {
            elementData=new Object[capacity];  
        }
        
    }
    public void add(E element){
        //什么时候扩容
        if(size==elementData.length){
            //怎么扩容,10+10/2,要把(elementData.length>>1) 因为+的优先级比>>1高
            Object[] newArray=new Object[elementData.length+(elementData.length>>1)];
            System.arraycopy(elementData,0,newArray,0,elementData.length);
            elementData=newArray;

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

    }

    public void set(E element,int index){
        checkRange(index);
        elementData[index]=element;
    }

    public  void  checkRange(int index){
        //所有合法的判断[0,size)
        if(index<0||index>size-1){
            throw  new  RuntimeException("索引越界了"+index);
        }

    }


    public static void main(String[] args) {
        SxtArraList s1=new SxtArraList(20);
        for(int i=0;i<40;i++){
            s1.add("小白");
        }
        System.out.println(s1);
        s1.set("小黑",1);
        System.out.println(s1);
        System.out.println(s1.get(10));
        System.out.println(s1.get(-1));
    }
}

第四版、增加remove、size等方法

package cn.zxg.collection;

/**
 * 自定义实现ArraList,体会底层原理
 * 1、增加get和set方法,索引合法的判断
 * 2、增加remove方法
 */

public class SxtArraList <E>{
    private int size;
    private  Object[] elementData;
    private static final int DEFALT_CAPACITY=10;
    public SxtArraList(){
        elementData=new Object[DEFALT_CAPACITY];
    }

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

    }
    public void add(E element){
        //什么时候扩容
        if(size==elementData.length){
            //怎么扩容,10+10/2,要把(elementData.length>>1) 因为+的优先级比>>1高
            Object[] newArray=new Object[elementData.length+(elementData.length>>1)];
            System.arraycopy(elementData,0,newArray,0,elementData.length);
            elementData=newArray;

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

    }

    public void set(E element,int index){
        checkRange(index);
        elementData[index]=element;
    }

    public  void  checkRange(int index){
        //所有合法的判断[0,size)
        if(index<0||index>size-1){
            throw  new  RuntimeException("索引越界了"+index);
        }

    }

    public void remove(E element){
        for(int i=0;i<size;i++){
            if(element.equals(get(i))){
                remove(i);
            }
        }
    }


    public  void remove(int index){
        //a,b,c,d,e,fg
        //a,b,c,e,f,g,h
        int numMoved=elementData.length-index-1;
        if(numMoved>0){
            System.arraycopy(elementData,index+1,elementData,index,numMoved);
        }
        elementData[--size]=null;


    }
    //获取容器大小
    public  int size(){
        return size;
    }
    //判断容器是否为空
    public  boolean isEmpty(){
        return size==0?true:false;
    }


    public static void main(String[] args) {
        SxtArraList s1=new SxtArraList(20);
        for(int i=0;i<40;i++){
            s1.add("小白"+i);
        }
        System.out.println(s1);
        s1.set("小黑",1);
        System.out.println(s1);
        System.out.println(s1.get(10));
//        System.out.println(s1.get(-1));
        s1.remove(3);
        s1.remove("小白");
        System.out.println(s1);
    }
}