clone()方法学习

Object中有个方法：

protected native Object clone() throws CloneNotSupportedException;

对于类X，现在有类X的一个实例xInstance

1、X没有实现java.lang.Cloneable

xInstance.clone();会抛出异常CloneNotSupportedException

2、X实现了java.lang.Cloneable

如果X在clone() 中只是调用super.clone()，则会有一个X的新实例xNewInstance（注意：生成xNewInstance时并不会调用构函），xNewInstance中域的值和xInstance中域是的值完全一样的，即xNewInstance是xInstance的一个浅copy（shadow copy)

 

package effectivejava.clone.Item10;import java.text.SimpleDateFormat;import java.util.Date;public class TestCloneFather {private StringBuffer sb = new StringBuffer();public TestCloneFather() {System.out.println("Father's constructor");sb.append(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss-SSS").format(new Date()));try {Thread.sleep(2000);} catch (InterruptedException e) {e.printStackTrace();}}public void display() {System.out.println("Father:" + sb);System.out.println("Father:" + sb.hashCode());}}

 

package effectivejava.clone.Item10;import java.text.SimpleDateFormat;import java.util.Date;final public class TestCloneSon extends TestCloneFather implements Cloneable {private final StringBuffer sb = new StringBuffer(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss-SSS").format(new Date()));public String[] arrayString = new String[10];public TestCloneSon() {System.out.println("Son's constructor");arrayString[0] = "libing0";arrayString[1] = "libing1";arrayString[2] = "libing2";}public void display() {super.display();System.out.println("Son:" + sb);System.out.println("Son:" + sb.hashCode());for (int i = 0; i < arrayString.length; i++) {System.out.print(arrayString[i] + ", ");}System.out.println();System.out.println("arrayString:" + arrayString.hashCode());}public Object clone() {try {TestCloneSon tc = (TestCloneSon) super.clone();tc.arrayString = arrayString.clone();tc.arrayString[9] = "libing9";return tc;} catch (CloneNotSupportedException e) {e.printStackTrace();}return null;}public static void main(String[] args) throws Exception {TestCloneSon tcs = new TestCloneSon();tcs.display();Thread.sleep(2000);System.out.println("After 2 second, begin clone");((TestCloneFather) tcs.clone()).display();}}

 

输出：

Father's constructor
Son's constructor
Father:2010-06-05 19:40:36-265
Father:9023134
Son:2010-06-05 19:40:38-265
Son:19336051
libing0, libing1, libing2, null, null, null, null, null, null, null,
arrayString:6336176
After 2 second, begin clone
Father:2010-06-05 19:40:36-265
Father:9023134
Son:2010-06-05 19:40:38-265
Son:19336051
libing0, libing1, libing2, null, null, null, null, null, null, libing9,
arrayString:6718604