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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;    }}