目录

• 数组复制
• 1. System.java
• 2. API

---

数组复制

• 用 java.lang.System 中的 static void arraycopy(Object src, int srcPos, Object dest, int destPos, int length)；

import java.util.Arrays;

public class Test {
    public static void main(String[] args) {
        int[] src = {1, 2, 3, 4, 5, 6, 7};
        int[] dest = new int[3];
        //arraycopy(Object src, int srcIndex, Object dest, int destIndex, int length);
        //srcIndex, destIndex都表示从哪个下标开始复制
        System.arraycopy(src,2,dest,0,3);
        System.out.println(Arrays.toString(dest));
    }
}
/*
输出
[3, 4, 5]
 */

---

1. System.java

• 用到了 关键字 native，native 主要用于方法上：
• 一个 native 方法就是一个 Java 调用非 Java 代码的接口。一个 native 方法是指该方法的实现由非 Java 语言实现，比如用 C 或 C++ 实现；
• 在定义一个 native 方法时，并不提供实现体（比较像定义一个Java Interface），因为其实现体是由非 Java 语言在外面实现的；
• 主要是因为 JAVA 无法对操作系统底层进行操作，但是可以通过 jni(java native interface) 调用其他语言来实现底层的访问；

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

    /**
     * Returns the same hash code for the given object as
     * would be returned by the default method hashCode(),
     * whether or not the given object's class overrides
     * hashCode().
     * The hash code for the null reference is zero.
     *
     * @param x object for which the hashCode is to be calculated
     * @return  the hashCode
     * @since   1.1
     * @see Object#hashCode
     * @see java.util.Objects#hashCode(Object)
     */

---

2. API

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

• Copies an array from the specified source array, beginning at the specified position, to the specified position of the destination array. A subsequence of array components are copied from the source array referenced by src to the destination array referenced by dest. The number of components copied is equal to the length argument. The components at positions srcPos through srcPos+length-1 in the source array are copied into positions destPos through destPos+length-1, respectively, of the destination array.
  If the src and dest arguments refer to the same array object, then the copying is performed as if the components at positions srcPos through srcPos+length-1 were first copied to a temporary array with length components and then the contents of the temporary array were copied into positions destPos through destPos+length-1 of the destination array.

• If dest is null, then a NullPointerException is thrown.

• If src is null, then a NullPointerException is thrown and the destination array is not modified.

• Otherwise, if any of the following is true, an ArrayStoreException is thrown and the destination is not modified:

• The src argument refers to an object that is not an array.
  The dest argument refers to an object that is not an array.
  The src argument and dest argument refer to arrays whose component types are different primitive types.
  The src argument refers to an array with a primitive component type and the dest argument refers to an array with a reference component type.
  The src argument refers to an array with a reference component type and the dest argument refers to an array with a primitive component type.
  Otherwise, if any of the following is true, an IndexOutOfBoundsException is thrown and the destination is not modified:

• The srcPos argument is negative.
  The destPos argument is negative.
  The length argument is negative.
  srcPos+length is greater than src.length, the length of the source array.
  destPos+length is greater than dest.length, the length of the destination array.
  Otherwise, if any actual component of the source array from position srcPos through srcPos+length-1 cannot be converted to the component type of the destination array by assignment conversion, an ArrayStoreException is thrown. In this case, let k be the smallest nonnegative integer less than length such that src[srcPos+k] cannot be converted to the component type of the destination array; when the exception is thrown, source array components from positions srcPos through srcPos+k-1 will already have been copied to destination array positions destPos through destPos+k-1 and no other positions of the destination array will have been modified. (Because of the restrictions already itemized, this paragraph effectively applies only to the situation where both arrays have component types that are reference types.)

• Parameters:
  src - the source array.
  srcPos - starting position in the source array.
  dest - the destination array.
  destPos - starting position in the destination data.
  length - the number of array elements to be copied.
  Throws:
  IndexOutOfBoundsException - if copying would cause access of data outside array bounds.
  ArrayStoreException - if an element in the src array could not be stored into the dest array because of a type mismatch.
  NullPointerException - if either src or dest is null.

标签：src,Java,dest,srcPos,int,length,复制,数组,array
来源： https://blog.csdn.net/Regino/article/details/104699311