Java 數組拷貝

Arrays.copyOf

public static int[] copyOf(int[] original, int newLength) {
     int[] copy = new int[newLength];
     System.arraycopy(original, 0, copy, 0, Math.min(original.length, newLength));
     return copy;
}      

方法其實就是傳回一個數組，而這個數組就等于數組array的前 newLength 數。

其實内部用了 System.arraycopy 方法

舉例：

int[] array = new int[]{1, 2, 3, 4, 5};
 int[] array2 = Arrays.copyOf(array, 3);
  
 //array2結果：[1,2,3]      

Arrays.copyOfRange

public static int[] copyOfRange(int[] original, int from, int to) {
        int newLength = to - from;
        if (newLength < 0)
            throw new IllegalArgumentException(from + " > " + to);
        int[] copy = new int[newLength];
        System.arraycopy(original, from, copy, 0,
                         Math.min(original.length - from, newLength));
        return copy;
    }      

複制原數組的一段值，長度是 ​

​to - from ​

​

舉例：

int[] array = new int[]{1, 2, 3, 4, 5};
 int[] array2 = Arrays.copyOfRange(array, 1,3);
  
 //array2 結果:[2,3]      

System.arraycopy

這是一個 native 方法

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

• src 源資料
• srcPos 源資料起始位置
• dest 目标資料
• destPos 目标資料其實位置
• length 複制的長度

String[] array = new String[]{"1", "2", "3", "4", "5"};
String[] array2 = new String[5];
array2[0] = "a";
array2[1] = "b";
array2[2] = "c";
System.arraycopy(array, 1, array2, 2, 2);

//array2 結果：["a", "b", "2", "3", null]