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Back-end/Java

[Java] ArrayList 사용 없이 개념 익히기

by 디팔⸜( ◜࿁◝ )⸝︎︎ 2022. 9. 6.
package com.example.MyJavaProject;

class Main {
    public static void main(String[] args) {
        ArrayList al = new ArrayList();

        System.out.println("al.size() : " + al.size());
        // 출력 => al.size() : 0


        al.add(100);

        System.out.println("al.get(0) : " + al.get(0));
        // 출력 => al.get(0) : 100

        al.add(200);
        al.add(300);

        System.out.println("al.size() : " + al.size());
        // 출력 => al.size() : 3

        System.out.println("al.get(1) : " + al.get(1));
        // 출력 => al.get(1) : 200

        al.removeAt(1);

        System.out.println("al.size() : " + al.size());
        // 출력 => al.size() : 2

        System.out.println("al.get(1) : " + al.get(1));
        // 출력 => al.get(1) : 300

        al.add(400);
        al.add(500);
        al.add(600);

        System.out.println("al.get(3) + al.get(4) : " + (al.get(3) + al.get(4)));
        // 출력 => al.get(3) + al.get(4) : 1100

        al.showAllValues();
        // 출력 =>
		/*
		== 전체 데이터 출력 ==
		0 : 100
		1 : 300
		2 : 400
		3 : 500
		4 : 600
		*/

        al.add(700, 1);
        al.add(750, 1);

        al.showAllValues();

    }
}

class ArrayList{
    int[] arr = new int[2];
    public int superIndex = 0;

    int size(){
        return superIndex;
    }

    void add(int value) {
        if (superIndex > 1) {
            int[] arrTmp = new int[superIndex + 1];
            for (int i = 0; i < superIndex; i++) {
                arrTmp[i] = arr[i];
            }
            arrTmp[superIndex] = value;
            arr = arrTmp;
        } else {
            arr[superIndex] = value;
        }
        superIndex++;
    }
    void add(int value, int index) {
        int[] arrTmp = new int[arr.length+1];
        for(int t=0; t<arrTmp.length; t++){
            if(t<index) {
                arrTmp[t] = arr[t];
            }else if(t==index){
                arrTmp[t] = value;
            }else if(t>index){
                arrTmp[t] = arr[t-1];
            }
        }
        arr = arrTmp;
        superIndex = arr.length;
    }



    int get(int index){
        return arr[index];
    }

    void removeAt(int index){
        int[] arrTmp = new int[arr.length-1];
        int k = 0;
        while(true){
            if(k<index) {
                arrTmp[k] = arr[k];
                k++;
            }else if(k>=index){
                arrTmp[k] = arr[k+1];
                k++;
            } else {
                return;
            }
            if(k==arrTmp.length){
                break;
            }
        }
        arr = arrTmp;
        superIndex = arr.length;
    }

    void showAllValues(){
        System.out.println("===전체 데이터 출력===");
        int j = 0;
        while(true){
            if(j==arr.length){break;}
            System.out.printf("%d : %d \n",j, arr[j]);
            j++;
        }
    }

}

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