Java ArrayList Shallow copy vs Deep copy

Shallow Copy(얕은 복사)

 

1) 소스와 타겟이 모두 추가/변경에 영향을 받음

ArrayList<Node> sourceList = new ArrayList<>();

ArrayList<Node> targetList = sourceList;

 

아래 2),3),4)는 추가는 소스만, 변경은 소스와 타켓 모두 영향을 받음

2)

ArrayList<Node> sourceList = new ArrayList<>();

ArrayList<Node> targetList = new ArrayList<>(sourceList);

 

3)

ArrayList<Node> targetList = new ArrayList<>();

targetList.addAll(sourceList);

 

4)

ArrayList<Node> sourceList = new ArrayList<>();

ArrayList<Node> targetList = (ArrayList<Node>)sourceList.clone();

 

2.Deep Copy(깊은 복사)

 

5)소스와 타겟의 데이터 추가 및 변경이 독립적

 

 

ArrayList<Node> sourceList = new ArrayList<>();

ArrayList <Node> targetList = new ArrayList<>();

for (Node node : sourceList) {
    Node newNode = new Node(node.data, node.name);
    targetList.add(newNode);
}

 

import java.util.ArrayList;

class Node {

    int data;
    String name;

    Node(int data, String name) {

        this.data = data;
        this.name = name;
    }

    public String toString() {

        return "{" + Integer.toString(data) + ", " + name + "}";
    }
}

public class ArrayListTest {
    public static void main(String[] args) {

        testCopy1();
        System.out.println("===============\n\n");
        testCopy2();
        System.out.println("===============\n\n");
        testCopy3();
        System.out.println("===============\n\n");
        testCopy4();
        System.out.println("===============\n\n");
        testCopy5();

    }

    static void testCopy1(){
        ArrayList<Node> sourceList = new ArrayList <Node>();

        Node node[] = new Node[5];
        for(int i = 0; i < 5; i++) {
            node[i] = new Node(i, Integer.toString(i));
        }

        sourceList.add(node[0]);
        sourceList.add(node[1]);
        sourceList.add(node[2]);

        System.out.println("Before1: ");
        System.out.println("sourceList = " + sourceList.toString());

        ArrayList <Node> targetList = sourceList;

        System.out.println("targetList = " + targetList.toString());

        sourceList.add(node[3]);//source, target 추가됨

        node[2].data = 10;
        node[2].name = "10";//source, target 변경됨

        System.out.println("\nAfter: ");
        System.out.println("sourceList = " + sourceList.toString());
        System.out.println("targetList = " + targetList.toString());
    }

    static void testCopy2(){
        ArrayList<Node> sourceList = new ArrayList <>();

        Node node[] = new Node[5];
        for(int i = 0; i < 5; i++) {
            node[i] = new Node(i, Integer.toString(i));
        }

        sourceList.add(node[0]);
        sourceList.add(node[1]);
        sourceList.add(node[2]);

        System.out.println("Before2: ");
        System.out.println("sourceList = " + sourceList.toString());

        ArrayList <Node> targetList = new ArrayList <> (sourceList);

        System.out.println("targetList = " + targetList.toString());

        sourceList.add(node[3]);//source만 추가됨

        node[2].data = 20;
        node[2].name = "20";//source, target변경됨

        System.out.println("\nCurrent2: ");
        System.out.println("sourceList = " + sourceList.toString());
        System.out.println("targetList = " + targetList.toString());
    }

    static void testCopy3(){
        ArrayList<Node> sourceList = new ArrayList <>();

        Node node[] = new Node[5];
        for(int i = 0; i < 5; i++) {
            node[i] = new Node(i, Integer.toString(i));
        }

        sourceList.add(node[0]);
        sourceList.add(node[1]);
        sourceList.add(node[2]);

        System.out.println("Before3: ");
        System.out.println("sourceList = " + sourceList.toString());

        ArrayList <Node> targetList = new ArrayList <> ();
        targetList.addAll(sourceList);

        System.out.println("targetList = " + targetList.toString());

        sourceList.add(node[3]);

        node[2].data = 30;
        node[2].name = "30";

        System.out.println("\nAfter3: ");
        System.out.println("sourceList = " + sourceList.toString());
        System.out.println("targetList = " + targetList.toString());
    }

     static void testCopy4(){
        ArrayList<Node> soureList = new ArrayList <Node>();

        Node node[] = new Node[5];
        for(int i = 0; i < 5; i++) {
            node[i] = new Node(i, Integer.toString(i));
        }

        soureList.add(node[0]);
        soureList.add(node[1]);
        soureList.add(node[2]);

        System.out.println("Before4: ");
        System.out.println("sourceList = " + soureList.toString());

        ArrayList <Node> targetList = (ArrayList <Node>)soureList.clone();

        System.out.println("targetList = " + targetList.toString());

        soureList.add(node[3]);

        node[2].data = 40;
        node[2].name = "40";

        System.out.println("\nAfter4: ");
        System.out.println("sourceList = " + soureList.toString());
        System.out.println("targetList = " + targetList.toString());
    }

    static void testCopy5(){
        ArrayList<Node> sourceList = new ArrayList <>();

        Node n[] = new Node[5];
        for(int i = 0; i < 5; i++) {
            n[i] = new Node(i, Integer.toString(i));
        }

        sourceList.add(n[0]);
        sourceList.add(n[1]);
        sourceList.add(n[2]);

        System.out.println("Before5: ");
        System.out.println("sourceList = " + sourceList.toString());

        ArrayList <Node> targetList = new ArrayList<>();

        for (Node node : sourceList) {
            Node newNode = new Node(node.data, node.name);
            targetList.add(newNode);
        }

        System.out.println("targetList = " + targetList.toString());

        sourceList.add(n[3]);//sourceList 만추가

        n[2].data = 50;
        n[2].name = "50";//sourceList만 변경

        System.out.println("\nAfter5: ");
        System.out.println("sourceList = " + sourceList.toString());
        System.out.println("targetList = " + targetList.toString());
    }
}