【Java】之 简易ArrayList

查看ArrayList的方法们（挑选几个）

源码

package dataStructure;

import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.regex.Pattern;

/**
 * Created by donal on 2017/2/12.
 */

/**
 * 输出方法体
 * Pattern p = Pattern.compile("\\w+\\.");
 try{
 Class<?> c = Class.forName("java.util.ArrayList");
 Method[] methods = c.getMethods();
 Constructor[] constructors = c.getConstructors();
 for(Method method : methods){
 System.out.println(
 p.matcher(method.toString()).replaceAll("")     //去掉 包名.类名.
 );
 }
 System.out.println("----------------------------------------------");
 for (Constructor constructor : constructors){
 System.out.println(p.matcher(constructor.toString()).replaceAll(""));
 }
 }catch (ClassNotFoundException e){
 System.out.println("No such class: " + e);
 }
 */
public class MyArrayList

    private static final int DEFAULT_CAPACITY = 10;
    private static final Object[] EMPTY_ELEMENTDATA = {};
    private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};
    transient Object[] elementData;
    private int size;

    public MyArrayList() {
        this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
    }

    public MyArrayList(int initialCapacity){
        if (initialCapacity > 0) {
            this.elementData = new Object[initialCapacity];
        } else if (initialCapacity == 0) {
            this.elementData = EMPTY_ELEMENTDATA;
        } else {
            throw new IllegalArgumentException("Illegal Capacity: "+
                    initialCapacity);
        }
    }

    private void makeSure(int capacitySize){
        if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA ){
            elementData = new Object[DEFAULT_CAPACITY];
        }else if (capacitySize > DEFAULT_CAPACITY){
            throw new RuntimeException();
        }
    }

    public boolean add(Object o){
        makeSure(size + 1);
        elementData[size++] = o;
        return true;
    }

    public void add(int index, Object o){
        if (index >= DEFAULT_CAPACITY)
            throw new RuntimeException();
        makeSure(size + 1);
        System.arraycopy(elementData, index, elementData, index + 1,
                size - index);
        elementData[index] = o;
        size++;
    }

    public boolean remove(Object o){
        int index = -1;
        for (int i = 0; i < size(); ++i){
            if (elementData[i] == o){
                index = i;
                break;
            }
        }
        if (index == -1)
            return false;
        else
            remove(index);
        return true;
    }

    public Object remove(int index){
        if (index >= DEFAULT_CAPACITY)
            throw new RuntimeException();
        Object oldElem = elementData[index];
        System.arraycopy(elementData, index, elementData, index,
                size - index);
        elementData[size--] = null;
        return oldElem;
    }

    public Object get(int n){
        if (n > size())
            throw new RuntimeException();

        return elementData[n];
    }

    public int indexOf(Object o){
        for (int i = 0; i < size(); ++i){
            if (elementData[i] == o)
                return i;
        }

        return -1;
    }

    public void clear(){
        for (int i = 0 ; i < size(); ++i)
            elementData[i] = null;
    }

    public boolean contains(Object o){
        for (int i = 0; i < size(); ++i){
            if (elementData[i] == o)
                return true;
        }
        return false;
    }

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

    public int size(){
        return size;
    }

    public String toString(){
        StringBuilder sb = new StringBuilder();
        for (int i = 0 ; i < size(); ++i){
            sb.append("index : " + i + ", element : " + elementData[i] + "\n");
        }
        return sb.toString();
    }
    public static void main(String[] args) {

        MyArrayList myArrayList = new MyArrayList(5);
        myArrayList.add("123");
        myArrayList.add("456");
        myArrayList.add("789");
        System.out.println(myArrayList.get(1));
        System.out.println(myArrayList.size());
        myArrayList.remove(2);
        System.out.println(myArrayList);
    }
}