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java杂记——数组拷贝
这里介绍两种java提供的数组拷贝方法:
(1)Arrays提供的copyOf(T src, T desLength)和copyOfRange(T src, int from, int to)
(2)System.arraycopy(T src, int from, T des, int from, int length)
使用例子:
(1)
int [] a = {1,2,3,4,5,6};
int [] b = Arrays.copyOf(a, 8); //把a拷贝到长度为8的b中。b的长度可比a长,长的部分补0;可比a短,把a截断。
int [] c = Arrays.copyOfRange(a, 2, 5); //把a的数组下标为2的到下标为5的前一个,拷贝到c中,c的长度为5-2=3。
(2)
int [] a = {1,2,3,4,5,6};
int [] b = new int[8];
System.arraycopy(a, 2, b, 3, 4); //把数组a从下标为2的元素开始,拷贝长度为4的元素到b中,从b的下标为3的位置开始放。
//如果b的位置不足以放下指定长度的元素,会报java.lang.ArrayIndexOutOfBoundsException异常
在方法(2)中,如果目标数组和源数组相同,则先拷贝到一个temp数组中,再从temp数组中拷回目标数组(源)。
当数组是对象数组的时候,上面的两种方法都不能实现深度拷贝。例如:源代码中的
Lesson9_arrayCopyTest.deepArrayCopy()
详细代码如下:
package javaBase16Lesson;import java.util.Arrays;/** * (1) * int [] a = {1,2,3,4,5,6}; * int [] b = Arrays.copyOf(a, 8); //把a拷贝到长度为8的b中。b的长度可比a长,长的部分补0;可比a短,把a截断。 * int [] c = Arrays.copyOfRange(a, 2, 5); //把a的数组下标为2的到下标为5的前一个,拷贝到c中,c的长度为5-2=3。 * *(2) * int [] a = {1,2,3,4,5,6}; * int [] b = new int[8]; * System.arraycopy(a, 2, b, 3, 4); //把数组a从下标为2的元素开始,拷贝长度为4的元素到b中,从b的下标为3的位置开始放。 * //如果b的位置不足以放下指定长度的元素,会报java.lang.ArrayIndexOutOfBoundsException异常 * *(3) *方法(1)(2)都只是数组的浅拷贝,无法实现深度拷贝 * @author cnx * @Description : arrayCopyTest * @CreateDate ; 2014年7月9日 下午6:43:26 */public class Lesson9_arrayCopyTest { public static void main(String[] args) {// Lesson9_arrayCopyTest.arraysCopyOf();// Lesson9_arrayCopyTest.systemArraycopy(); Lesson9_arrayCopyTest.deepArrayCopy(); } public static void arraysCopyOf(){ int [] a = {1,2,3,4,5,6}; int [] b = Arrays.copyOf(a, 8); //把a拷贝到长度为8的b中。b的长度可比a长,长的部分补0;可比a短,把a截断。 int [] c = Arrays.copyOfRange(a, 2, 5); //把a的数组下标为2的到下标为5的前一个,拷贝到c中,c的长度为5-2=3。 System.out.println("a:"+ a.length); for (int i = 0; i < a.length; i++) { System.out.println(a[i]); } System.out.println("b:"+ b.length); for (int i : b) { System.out.println(i); } System.out.println("c:"+ c.length); for (int i : c) { System.out.println(i); } } /** * 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. <br> * 如果目标数组和源数组相同,则先拷贝到一个temp数组中,再从temp数组中拷回目标数组(源) */ public static void systemArraycopy(){ int [] a = {1,2,3,4,5,6}; int [] b = new int[8]; System.arraycopy(a, 2, b, 3, 4); //把数组a从下标为2的元素开始,拷贝长度为4的元素到b中,从b的下标为3的位置开始放。 //如果b的位置不足以放下指定长度的元素,会报java.lang.ArrayIndexOutOfBoundsException异常 System.out.println("a:"+ a.length); for (int i = 0; i < a.length; i++) { System.out.println(a[i]); } System.out.println("b:"+ b.length); for (int i : b) { System.out.println(i); } } /** * 上面的两种方法都无法实现深度拷贝 */ public static void deepArrayCopy(){ Lesson9_array1 [] a1 = {new Lesson9_array1(),new Lesson9_array1()}; Lesson9_array1 [] a2 = null; Lesson9_array1 [] a3 = new Lesson9_array1[3]; Lesson9_array2 [] b1 = {new Lesson9_array2(),new Lesson9_array2()}; Lesson9_array2 [] b2 = null; a2 = Arrays.copyOf(a1, 3); System.arraycopy(a1, 0, a3, 0, 2); b2 = Arrays.copyOf(b1, 3); a1[1].a = "a1"; System.out.println(a2[1].a); System.out.println(a3[1].a); b1[1].a = "b1"; System.out.println(b2[1].a); }}class Lesson9_array1 implements Cloneable{ public String a = "deep"; public Object clone(){ Object o = null; try { o = (Lesson9_array1)super.clone(); } catch (CloneNotSupportedException e) { e.printStackTrace(); } return o; } public String toString(){ return a; }}class Lesson9_array2{ public String a = "deep"; public String toString(){ return a; }}
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