Arrays.copyOfRange方法

•  Arrays.copyOfRange方法源码，本质是调用了System.arraycopy方法

* @param original the array from which a range is to be copied 原数组
* @param from the initial index of the range to be copied, inclusive 从下标为from的元素开始拷贝，包括该元素
* @param to the final index of the range to be copied, exclusive。截至到下标为to的元素，不包括该元素
　　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;
    }

• 需要注意的事项

1.  如果 from > to 会抛出 IllegalArgumentException异常

 

     //代码 
     int[] a=new int[]{1,2,3};
     System.out.println(Arrays.toString(Arrays.copyOfRange(a,1,0)));  
    //结果
 Exception in thread "main" java.lang.IllegalArgumentException: 1 > 0
    at java.base/java.util.Arrays.copyOfRange(Arrays.java:4101)
    at test.test.main(test.java:11)

 

2. from > to ，会复制原数组下标区间为 [ from,to )范围内的元素

 

     //代码 
     int[] a=new int[]{1,2,3};
     System.out.println(Arrays.toString(Arrays.copyOfRange(a,1,3)));  
    //结果
    [2,3]

 

3. from = to ，会返回空数组

 

     //代码 
     int[] a=new int[]{1,2,3};
     System.out.println(Arrays.toString(Arrays.copyOfRange(a,1,1)));  
    //结果
    []

 

4. to > 数组总长度，超出的部分会补0

 

     //代码 
     int[] a=new int[]{1,2,3};
     System.out.println(Arrays.toString(Arrays.copyOfRange(a,1,5)));  
    //结果
　　[2, 3, 0, 0]