JAVA array copy method
1. Use a for loop to traverse, which is the least efficient
int [] arr = {1,2,3,4,5,6,7,8}; int [] arr1 = new int [arr.length]; for (int i = 0; i <arr.length ; i++) { arr1[i]=arr[i]; } System.out.println(Arrays.toString(arr1)); //结果[1, 2, 3, 4, 5, 6, 7, 8]
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2. Use the methods provided in Arrays
2.1copyof() is less efficient than the third method
// orinigal表示要复制的数组;newlength表示要复制的长度,如果newlength>original.length,多出的部分将以数组默认值的方式给出 public static int[] copyOf(int[] original,int newLength) int [] arr = {1,2,3,4,5,6,7,8}; int [] arr2 = Arrays.copyOf(arr,3); System.out.println(Arrays.toString(arr2));// 输出 [1, 2, 3]
2.2copyOfRange() copies an array of specified length
public static <T> T[] copyOfRange(T[] original,int from,int to) // 左闭右开// T - 数组中对象的类 // original - 要从中复制范围的数组 // from - 要复制的范围的初始索引(包括) // to - 要复制的范围的最终索引,不包括。 (该索引可能位于数组之外) int [] arr = {2,5,4,6,8,7}; int [] arr2 = Arrays.copyOfRange(arr,1,7); System.out.println(Arrays.toString(arr2));// 输出[2, 3, 4, 5, 6, 7] // 当 to 的值为 9 时,此时超出了原数组的长度,结果为[2, 3, 4, 5, 6, 7, 8, 0]
3. System.arraycopy() is the most efficient
public static void arraycopy(Object src,int srcPos,Object dest,int destPos,int length) // src - 源数组。 // srcPos - 源数组中的起始位置。 // dest - 目标数组。 // destPos - 目的地数据中的起始位置。 // length - 要复制的数组元素的数量。 int [] arr = {1,2,3,4,5,6,7,8}; int [] arr3=new int [arr.length]; System.arraycopy(arr,1,arr3,2,5); System.out.println(Arrays.toString(arr3)); // 结果[0, 0, 2, 3, 4, 5, 6, 0]
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