参考链接： Java复制数组
文章目录
一维数组for循环拷贝数值类型拷贝引用类型
clone()拷贝数值方式拷贝引用类型
System.arraycopy()拷贝数值类型拷贝引用类型
Arrays.copyof()拷贝数值类型拷贝引用类型
二维数组for循环拷贝数值类型拷贝引用类型
clone()拷贝数值类型拷贝引用类型
System.arraycopy()拷贝数值类型拷贝引用类型
Arrays.copyof()拷贝数值类型拷贝引用类型
源码分析forclone()System.arraycopy()Arrays.copyof()
数组的拷贝方式有四种，分别是：
for循环 clone() System.arraycopy() Arrays.copyof()
一维数组
for循环
拷贝数值类型
int[] array = {1,2,3,4,5,6};
int[] array2 = new int[6];
for (int i = 0; i < array.length; i ) {
array2[i] = array[i];
}
System.out.println("拷贝数值类型：");
System.out.println(Arrays.toString(array));
System.out.println(Arrays.toString(array2));
System.out.println("--------------修改后--------------------");
array2[0] = 0;
System.out.println(Arrays.toString(array));
System.out.println(Arrays.toString(array2));
下面是运行结果：
拷贝引用类型
public class Arraycopy {
public static void main(String[] args) {
TestArray[] arrays = new TestArray[4];
arrays[0] = new TestArray(1);
arrays[1] = new TestArray(2);
arrays[2] = new TestArray(3);
arrays[3] = new TestArray(4);
TestArray[] arrays2 = new TestArray[4];
for (int i = 0; i < arrays.length; i ) {
arrays2[i] = arrays[i];
}
System.out.println("拷贝引用类型：");
show(arrays);
show(arrays2);
System.out.println("--------------修改后--------------------");
arrays2[0].setData(0);
show(arrays);
show(arrays2);
}
public static void show(TestArray[] arrays) {
for (int i = 0; i < arrays.length; i ) {
System.out.print(arrays[i].getData() " ");
}
System.out.println();
}
}
class TestArray {
private int data;
public TestArray(int data) {
this.data = data;
}
public int getData() {
return data;
}
public void setData(int data) {
this.data = data;
}
}
clone()
拷贝数值方式
int[] array = {1,2,3,4,5,6};
int[] array2 = new int[6];
array2 = array.clone();
System.out.println("拷贝数值类型：");
System.out.println(Arrays.toString(array));
System.out.println(Arrays.toString(array2));
System.out.println("--------------修改后--------------------");
array2[0] = 0;
System.out.println(Arrays.toString(array));
System.out.println(Arrays.toString(array2));
拷贝引用类型
TestArray[] arrays = new TestArray[4];
arrays[0] = new TestArray(1);
arrays[1] = new TestArray(2);
arrays[2] = new TestArray(3);
arrays[3] = new TestArray(4);
TestArray[] arrays2 = new TestArray[4];
arrays2 = arrays.clone();
System.out.println("拷贝引用类型：");
show(arrays);
show(arrays2);
System.out.println("--------------修改后--------------------");
arrays2[0].setData(0);
show(arrays);
show(arrays2);
System.arraycopy()
拷贝数值类型
int[] array = {1,2,3,4,5,6};
int[] array2 = new int[6];
System.arraycopy(array,0,array2,0,array.length);
System.out.println("拷贝数值类型：");
System.out.println(Arrays.toString(array));
System.out.println(Arrays.toString(array2));
System.out.println("--------------修改后--------------------");
array2[0] = 0;
System.out.println(Arrays.toString(array));
System.out.println(Arrays.toString(array2));
拷贝引用类型
TestArray[] arrays = new TestArray[4];
arrays[0] = new TestArray(1);
arrays[1] = new TestArray(2);
arrays[2] = new TestArray(3);
arrays[3] = new TestArray(4);
TestArray[] arrays2 = new TestArray[arrays.length];
System.arraycopy(arrays,0,arrays2,0,arrays.length);
arrays2 = arrays.clone();
System.out.println("拷贝引用类型：");
show(arrays);
show(arrays2);
System.out.println("--------------修改后--------------------");
arrays2[0].setData(0);
show(arrays);
show(arrays2);
Arrays.copyof()
拷贝数值类型
int[] array = {1,2,3,4,5,6};
int[] array2 = new int[6];
array2 = Arrays.copyOf(array,array.length);
System.out.println("拷贝数值类型：");
System.out.println(Arrays.toString(array));
System.out.println(Arrays.toString(array2));
System.out.println("--------------修改后--------------------");
array2[0] = 0;
System.out.println(Arrays.toString(array));
System.out.println(Arrays.toString(array2));
拷贝引用类型
TestArray[] arrays = new TestArray[4];
arrays[0] = new TestArray(1);
arrays[1] = new TestArray(2);
arrays[2] = new TestArray(3);
arrays[3] = new TestArray(4);
TestArray[] arrays2 = new TestArray[4];
arrays2 = Arrays.copyOf(arrays,arrays.length);
System.out.println("拷贝引用类型：");
show(arrays);
show(arrays2);
System.out.println("--------------修改后--------------------");
arrays2[0].setData(0);
show(arrays);
show(arrays2);
二维数组
for循环
拷贝数值类型
int[][] array = {{1,2,3},{4,5,6}};
int[][] array2 = new int[2][3];
for (int i = 0; i < array.length; i ) {
for (int j = 0; j < array[i].length; j ) {
array2[i][j] = array[i][j];
}
}
System.out.println("拷贝数值类型：");
System.out.println(Arrays.deepToString(array));
System.out.println(Arrays.deepToString(array2));
System.out.println("--------------修改后--------------------");
array2[0][0] = 0;
System.out.println(Arrays.deepToString(array));
System.out.println(Arrays.deepToString(array2));
拷贝引用类型
public class TwoArrayCopy {
public static void main(String[] args) {
TestArray[][] arrays = new TestArray[2][2];
arrays[0][0] = new TestArray(1);
arrays[0][1] = new TestArray(2);
arrays[1][0] = new TestArray(3);
arrays[1][1] = new TestArray(4);
TestArray[][] arrays2 = new TestArray[2][2];
for (int i = 0; i < arrays.length; i ) {
for (int j = 0; j < arrays[i].length; j ) {
arrays2[i][j] = arrays[i][j];
}
}
System.out.println("拷贝引用类型：");
show(arrays);
show(arrays2);
System.out.println("--------------修改后--------------------");
arrays2[0][0].setData(0);
show(arrays);
show(arrays2);
}
public static void show(TestArray[][] arrays) {
for (int i = 0; i < arrays.length; i ) {
for (int j = 0; j < arrays[i].length; j ) {
System.out.print(arrays[i][j].getData() " ");
}
System.out.println();
}
}
}
class TestArray {
private int data;
public TestArray(int data) {
this.data = data;
}
public int getData() {
return data;
}
public void setData(int data) {
this.data = data;
}
}
clone()
拷贝数值类型
int[][] array = {{1,2,3},{4,5,6}};
int[][] array2 = new int[2][3];
for (int i = 0; i < array.length; i ) {
array2[i] = array[i].clone();
}
System.out.println("拷贝数值类型：");
System.out.println(Arrays.deepToString(array));
System.out.println(Arrays.deepToString(array2));
System.out.println("--------------修改后--------------------");
array2[0][0] = 0;
System.out.println(Arrays.deepToString(array));
System.out.println(Arrays.deepToString(array2));
拷贝引用类型
TestArray[][] arrays = new TestArray[2][2];
arrays[0][0] = new TestArray(1);
arrays[0][1] = new TestArray(2);
arrays[1][0] = new TestArray(3);
arrays[1][1] = new TestArray(4);
TestArray[][] arrays2 = new TestArray[2][2];
for (int i = 0; i < arrays.length; i ) {
arrays2[i] = arrays[i].clone();
}
System.out.println("拷贝引用类型：");
show(arrays);
show(arrays2);
System.out.println("--------------修改后--------------------");
arrays2[0][0].setData(0);
show(arrays);
show(arrays2);
System.arraycopy()
拷贝数值类型
int[][] array = {{1,2,3},{4,5,6}};
int[][] array2 = new int[2][3];
for (int i = 0; i < array.length; i ) {
System.arraycopy(array[i],0,array2[i],0,array[i].length);
}
System.out.println("拷贝数值类型：");
System.out.println(Arrays.deepToString(array));
System.out.println(Arrays.deepToString(array2));
System.out.println("--------------修改后--------------------");
array2[0][0] = 0;
System.out.println(Arrays.deepToString(array));
System.out.println(Arrays.deepToString(array2));
拷贝引用类型
TestArray[][] arrays = new TestArray[2][2];
arrays[0][0] = new TestArray(1);
arrays[0][1] = new TestArray(2);
arrays[1][0] = new TestArray(3);
arrays[1][1] = new TestArray(4);
TestArray[][] arrays2 = new TestArray[2][2];
for (int i = 0; i < arrays.length; i ) {
System.arraycopy(arrays[i],0,arrays2[i],0,arrays[i].length);
}
System.out.println("拷贝引用类型：");
show(arrays);
show(arrays2);
System.out.println("--------------修改后--------------------");
arrays2[0][0].setData(0);
show(arrays);
show(arrays2);
Arrays.copyof()
拷贝数值类型
int[][] array = {{1,2,3},{4,5,6}};
int[][] array2 = new int[2][3];
for (int i = 0; i < array.length; i ) {
array2[i] = Arrays.copyOf(array[i],array[i].length);
}
System.out.println("拷贝数值类型：");
System.out.println(Arrays.deepToString(array));
System.out.println(Arrays.deepToString(array2));
System.out.println("--------------修改后--------------------");
array2[0][0] = 0;
System.out.println(Arrays.deepToString(array));
System.out.println(Arrays.deepToString(array2));
拷贝引用类型
TestArray[][] arrays = new TestArray[2][2];
arrays[0][0] = new TestArray(1);
arrays[0][1] = new TestArray(2);
arrays[1][0] = new TestArray(3);
arrays[1][1] = new TestArray(4);
TestArray[][] arrays2 = new TestArray[2][2];
for (int i = 0; i < arrays.length; i ) {
arrays2[i] = Arrays.copyOf(arrays[i],arrays[i].length);
}
System.out.println("拷贝引用类型：");
show(arrays);
show(arrays2);
System.out.println("--------------修改后--------------------");
arrays2[0][0].setData(0);
show(arrays);
show(arrays2);
源码分析
for
for循环是一种很灵巧的数组拷贝方式，经常可以自己封装成方法去使用。
clone()
克隆方法我们在数组中是找不到的，它是object的方法，我们先看看源码
protected native Object clone() throws CloneNotSupportedException;
看到了修饰符native，说明是由c或者c 实现的，它的优点是速度快，它返回了object对象，所以使用的时候需要用对象接收返回值。
System.arraycopy()
通过System类调用的静态方法，我们先看看源码
public static native void arraycopy(Object src, int srcPos,
Object dest, int destPos,
int length);
先来解释一下这些形参代表的意思，src代表被拷贝的对象，srcPos代表起始位置，dest代表目标对象，destpost代表目标对象的起始位置，length代表拷贝的长度。我们看到也是native修饰的，所以底层也是用c或者c 实现的，但是可以看到没有返回值，clone()还需要对返回值进行类型转换，所以它的速度是要比clone()要快的，这也是牛客网的一道题，问的就是四种拷贝哪种是最快的，答案肯定是System.arraycopy()。
Arrays.copyof()
这个方法是属于Arrays类的，我们先来看看源码是怎样实现的,在源码中提供了很多方法的重载，无非就是对于类型的一些替换，比如int数组，byte数组等等，就不一一列举了，我们写出常用的一个方法
public static int[] copyOf(int[] original, int newLength) {
int[] copy = new int[newLength];
System.arraycopy(original, 0, copy, 0,
Math.min(original.length, newLength));
return copy;
}
我们可以看到，在方法内部调用了System.arraycopy()，只是相当于重写了一下，换了一个名字。解释一下形参，original是待拷贝对象，newLength表示拷贝的长度，当然还有Arrays.copyOfRange(),就是可以控制拷贝的范围，不过我认为可以常用System.arraycopy(),这样什么情况都可以解决。
