Java中對象的淺拷貝與深拷貝

淺拷貝：拷貝對象與原始對中的引用類型引用同一個對象(指針指向同一個對象)

public class CloneDemo implements Cloneable{
    private int[] arr;

    public CloneDemo(){
        arr = new int[10];
        for (int i = 0; i < arr.length; i++) {
            arr[i] = i;
        }
    }
    public void set(int index, int value) {
        arr[index] = value;
    }

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

    /**
     * 淺拷貝：拷貝對象與原始對中的引用類型引用同一個對象(指針指向同一個對象)
     *
    @Override
    protected DeepCloneDemo clone() throws CloneNotSupportedException {
        return (DeepCloneDemo) super.clone();
    }
    */

深拷貝: 拷貝對象和原始對象中的引用類型引用(指針指向)不同對象

 /**
     * 深拷貝: 拷貝對象和原始對象中的引用類型引用(指針指向)不同對象
     * @return
     * @throws CloneNotSupportedException
     */
    @Override
    protected CloneDemo clone() throws CloneNotSupportedException {
        CloneDemo res =  (CloneDemo) super.clone();
        res.arr = new int[arr.length];  //指針指向了新的內存空間
        for (int i = 0; i < arr.length; i++) {
            res.arr[i] = arr[i];
        }
        return res;
    }

    public static void main(String[] args) {
        CloneDemo e1 = new CloneDemo();
        CloneDemo e2 = null;
        try {
            e2 = e1.clone();
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
        e1.set(2, 222);
        System.out.println(e2.get(2)); // 222
        e2.set(2,111);
        System.out.println(e1.get(2)); // 111
        System.out.println(e1);
        System.out.println(e2);
    }
}

這種方式的缺點：拷貝一個對象即複雜又有風險，它會拋出異常，並且還需要類型轉換。

使用拷貝構造函數或者拷貝工廠來拷貝對象

public class CloneConstructorDemo {
    /**
     * 最好使用拷貝構造函數或者拷貝工廠來拷貝對象，安全。
     */
    private int[] arr;

    public CloneConstructorDemo(){
        arr = new int[10];  //this.arr
        for (int i = 0; i < arr.length; i++) {
            arr[i] = i;
        }
    }

    public CloneConstructorDemo(CloneConstructorDemo original){
        arr = new int[original.arr.length]; //e2.arr = new int[e1.arr.length];
        for (int i = 0; i < original.arr.length; i++) {
            arr[i] = original.arr[i];
        }
    }

    public void setValue(int index, int value) {
        arr[index] = value;
    }

    public int getValue(int index) {
        return arr[index];
    }

    public static void main(String[] args) {
        CloneConstructorDemo e1 = new CloneConstructorDemo();
        CloneConstructorDemo e2 = new CloneConstructorDemo(e1);

        e1.setValue(2,11);
        System.out.println(e2.getValue(2));
    }
}