[Java] ArrayList 구현 - get(), add(), remove(), toString()

MyArrayList.java

public class MyArrayList {
	int initCapacity = 10;
	int[] elementData;
	int size; // # of data added
	int currentCapacity;
	int result;

	public MyArrayList() {
		elementData = new int[initCapacity];
		size=0;
		currentCapacity = initCapacity;
	}
	
	public int get(int index) {
		return elementData[index];
	}
	
	
	public void add(int data) {
		if(size == currentCapacity) {
			// array size 확대 <== 2배 크기의 array 를 만들어서 기존 data copy한 뒤 새 data를 추가 
			int [] newArray = new int [currentCapacity*2];
			for(int i=0; i<size; i++) {
				newArray[i]= elementData[i];
			}
			elementData = newArray;
			currentCapacity = currentCapacity*2;
		}else {
			elementData[size] = data;
			size++;
		}
	}
	
	public void add(int index , int data) {
		if(size != currentCapacity) {
			int [] newArray = new int [currentCapacity*2];
			for(int i=size; i>=index; i--) {
				newArray[i+1]= elementData[i];
			}
			for(int k=0; k<=index; k++){
				newArray[k] = elementData[k];
			}
			++size;
			++currentCapacity;
			elementData = newArray;
			elementData[index] = data;
		}
	}
	
	public int remove(int index) {
		int data = elementData[index];
		this.removeValue(index, data);
		return elementData[index];
	}

	
	public void removeValue(int index, int data) {
		if(size != currentCapacity){
			int [] newArray = new int [currentCapacity*2];
			for(int i=size; i>index; i--){
				newArray[i-1] = elementData[i];
			}
			for(int k=0; k<index; k++){
				newArray[k] = elementData[k];
			}
			--size;
			--currentCapacity;
			elementData = newArray;
		}
	}
	
	public int sizeOf() {
		return size;
	}
	
	public int arrSize() {
		return currentCapacity;
	}
	
	public String toString() {
		String ret = "";
		for(int i=0; i<size; i++)
			ret = ret + elementData[i] + ", ";
		return ret;
	}
	

}

 

 

MyArrayListMain.java

import java.util.ArrayList;
import java.util.Random;

public class MyArrayListMain {

	public static void main(String[] args) {
		
		Random random = new Random() ;
		int index = 3;
		int value = 77;


		MyArrayList me = new MyArrayList();

		for(int i=0; i<20; i++) {
		me.add((int) random.nextInt(99));
		}

	
		System.out.println(me.toString() + "---- [arraySize: " + me.arrSize() + "]");
		System.out.println(index + "번 인덱스 값: " + me.get(index));

		me.add(index, value);

		System.out.println();
		System.out.println(index + "번 인덱스에 " +value+ "을 추가합니다.");
		
		System.out.println();
		System.out.println(me.toString() + "---- [arraySize: " + me.arrSize() + "]");
		System.out.println(index + "번 인덱스 값: " + me.get(index));

		System.out.println();
		System.out.println(index+ "번 인덱스 값을 삭제합니다. ") ;
		me.remove(index);

		System.out.println();
		System.out.println(me.toString() + "---- [arraySize: " + me.arrSize() + "]");
		System.out.println(index + "번 인덱스 값: " + me.get(index));
	}
	
}