數組拷貝引發的思考

數組拷貝的三種方式

1.引用賦值

int[] a = {1,2,3,4,5};
int[] b = a;
a[0] = -1;
System.out.println(b[0]);   //-1

數組是用堆去保存的，賦值的時候只是把地址拷貝過去，兩個引用指向了同一個地址，所以改變任一數組中的值，另一個數組也會出現相應的變化。

2.數組遍歷賦值

int[] arr1 = {1,2,3};
int[] arr2 = new int[3];
int j = 0;
for(int i : arr1){
    arr[j++] = i;
}
//這個時候改變arr1[0]  = 3;那麼輸出arr2[0]還是等於1

3.clone()、Arrays.copyOf()、System.arraycopy()

從測試結果來看，以上三者都是屬於淺拷貝.

java中的深拷貝與淺拷貝

淺拷貝：對基本數據類型進行值傳遞，對引用數據類型進行引用傳遞般的拷貝，此爲淺拷貝。

深拷貝：對基本數據類型進行值傳遞，對引用數據類型，創建一個新的對象，並複製其內容，此爲深拷貝。

對於基本類型數組：

public void test4() {
    //該方式比較特殊,兩個引用指向同一個地址
    int[] lNumbers1 = new int[5];
    int[] rNumbers1 = lNumbers1;
    rNumbers1[0] = 1;
    boolean first = lNumbers1[0] == rNumbers1[0];
    Log.d("lNumbers1[0]=" + lNumbers1[0] + ",rNumbers1[0]=" + rNumbers1[0]+"---"+first);

    int[] lNumbers2 = new int[5];
    int[] rNumbers2 = Arrays.copyOf(lNumbers2, lNumbers2.length);
    rNumbers2[0] = 1;
    boolean second = lNumbers2[0] == rNumbers2[0];
    Log.d("lNumbers2[0]=" + lNumbers2[0] + ",rNumbers2[0]=" + rNumbers2[0]+"---"+second);

    int[] lNumbers3 = new int[5];
    int[] rNumbers3 = lNumbers3.clone();
    rNumbers3[0] = 1;
    boolean third = lNumbers3[0] == rNumbers3[0];
    Log.d( "lNumbers3[0]=" + lNumbers3[0] + ",rNumbers3[0]=" + rNumbers3[0]+"---"+third);
}

打印結果：

lNumbers1[0]=1,rNumbers1[0]=1---true
lNumbers2[0]=0,rNumbers2[0]=1---false
lNumbers3[0]=0,rNumbers3[0]=1---false

對於引用數據類型數組:

public static void test5() {
    People[] lNumbers1 = new People[5];
    lNumbers1[0] = new People();
    People[] rNumbers1 = lNumbers1;
    boolean first = lNumbers1[0].equals(rNumbers1[0]);
    Log.d("小楊逗比", "lNumbers1[0]=" + lNumbers1[0] + ",rNumbers1[0]=" + rNumbers1[0]+"--"+first);

    People[] lNumbers2 = new People[5];
    lNumbers2[0] = new People();
    People[] rNumbers2 = Arrays.copyOf(lNumbers2, lNumbers2.length);
    boolean second = lNumbers2[0].equals(rNumbers2[0]);
    Log.d("小楊逗比", "lNumbers2[0]=" + lNumbers2[0] + ",rNumbers2[0]=" + rNumbers2[0]+"--"+second);

    People[] lNumbers3 = new People[5];
    lNumbers3[0] = new People();
    People[] rNumbers3 = lNumbers3.clone();
    boolean third = lNumbers3[0].equals(rNumbers3[0]);
    Log.d("小楊逗比", "lNumbers3[0]=" + lNumbers3[0] + ",rNumbers3[0]=" + rNumbers3[0]+"--"+third);
}

public static class People implements Cloneable {

    int age;
    Holder holder;

    @Override
    protected Object clone() {
        try {
            return super.clone();
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
        return null;
    }

    public static class Holder {
        int holderValue;
    }
}

打印結果如圖：

lNumbers1[0]=org.yczbj.ycrefreshview.MainActivity$People@46a2c18,rNumbers1[0]=org.yczbj.ycrefreshview.MainActivity$People@46a2c18--true
lNumbers2[0]=org.yczbj.ycrefreshview.MainActivity$People@d344671,rNumbers2[0]=org.yczbj.ycrefreshview.MainActivity$People@d344671--true
lNumbers3[0]=org.yczbj.ycrefreshview.MainActivity$People@91e9c56,rNumbers3[0]=org.yczbj.ycrefreshview.MainActivity$People@91e9c56--true

另外，集合的拷貝也是我們平時經常會遇到的，一般情況下，我們都是用淺拷貝來實現，即通過構造函數或者clone方法。

深拷貝與淺拷貝裏講解的很全面了