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How to copy array in java

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2020-05-06 16:17:052769browse

How to copy array in java

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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