【Java】數組拷貝的三種方式

System.arraycopy

public static void arraycopy(Object src, int srcPos, Object dest, int destPos, int length);

src：原數組對象

srcPos：原數組起始位置

dest：目标數組對象

destPos：目标數組起始位置

length：複制長度

注意不要以為src和dest是Object類型，就可以随便傳參，不是數組對象會報錯。

該方法有一個一維數組、二維數組複制的差別，一維數組拷貝其值，二維數組拷貝引用，具體原理我将不清楚，有興趣可以運作如下代碼。

public class SystemArrayCopy {

    public static void main(String[] args) {
        int[] arr1 = {, , };
        int[] arr2 = new int[];

        System.arraycopy(arr1, , arr2, , arr2.length);
        for (int i = ; i < arr2.length; i++) {
            System.out.print(arr2[i] + " ");
        }

        System.out.println();

        String[] sArr1 = {"China", "Japan", "Korea"};
        String[] sArr2 = new String[];
        System.arraycopy(sArr1, , sArr2, , sArr2.length);
        for (int i = ; i < sArr2.length; i++) {
            System.out.print(sArr2[i] + " ");
        }

        System.out.println();

        sArr1[] = "USA";
        for (int i = ; i < sArr2.length; i++) {
            System.out.print(sArr2[i] + " ");
        }

        System.out.println();

        String[][] ss1 = {{"sh", "js", "zj"}, {"bj", "tj", "hb"}, {"sc", "cq", "yn"}};
        String[][] ss2 = new String[ss1.length][ss1[].length];
        System.arraycopy(ss1, , ss2, , ss1.length);
        for (int i = ; i < ss2.length; i++) {
            for (int j = ; j < ss2[i].length; j++)
                System.out.print(ss2[i][j] + " ");

            System.out.println();
        }

        System.out.println();

        ss1[][] = "dsh";
        for (int i = ; i < ss2.length; i++) {
            for (int j = ; j < ss2[i].length; j++)
                System.out.print(ss2[i][j] + " ");

            System.out.println();
        }
    }

}
           

Arrays.copyOf

Arrays.copyOf()重載了很多類型，以int型為例

public static int[] copyOf(int[] original, int newLength);

original：原數組

newLength：複制長度

傳回新複制的數組對象

分析Arrays的源代碼可知底層實際上是調用System.arraycopy()

Object.clone

在Java中，數組也是一種對象，是以可以使用clone()方法。

String[] sArr1 = {"China", "Japan", "Korea"};
String[] sArr2;
sArr2 = sArr1.clone();

for (int i = ; i < sArr2.length; i++) {
     System.out.print(sArr2[i] + " ");
}