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作者

请教一个StringBuffer 问题!!!!!!!!!!!!!

jancyu2008

发贴: 36
积分: 0

于 2008-06-24 21:34


public class Foo{
public static void main(String[] sgf){
  
  StringBuffer a = new StringBuffer("A");
  StringBuffer b = new StringBuffer("B");
  
  operate(a,b);
  
  System.out.println(a+","+b);//这里要求不能有变动
}

static void operate(StringBuffer x,StringBuffer y){
  
    x.append(y);
    y=x;
}
}

输入的结果如何才能变成AB,AB
而不是AB,B

jancyu2008 edited on 2008-06-28 00:07

Every day thinking about JAVA, because I like to
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作者

Re:请教一个StringBuffer 问题!!!!!!!!!!!!! [Re:jancyu2008]

JiafanZhou

版主

发贴: 736
积分: 61

于 2008-06-25 16:59

String Buffer is thread-safe, mutable sequence of characters. A string buffer is like a String, but can be modified.

Having said that, I can see where your confusion is, there is an important theory in Java concerning method invocation:
The local method parameter's object reference will *not* affect the object reference which invokes this method. (Because Java parameter is passed by value, not reference. aka completely two different spaces in memory)
However changing members of the object reference will be affected.

The above explanation sounds intimidating, but it actually not. In your example, object reference x has affected the value by invoking the append method, whereas object reference y does not. So you should avoid using the "=" sign because *it does not take any effect*.

> 输入的结果如何才能变成AB,AB


x.append( y );
y.delete(0, y.length());
y.append(x.toString());

Note this example does not have any practical use, it is only used for demonstrating the method invocation in Java.

Regards,
Jiafan

When I was a kid I used to pray every night for a new bike. Then I realized that The Lord doesn't work that way, so I stole one and asked him to forgive me.

作者

Re:请教一个StringBuffer 问题!!!!!!!!!!!!! [Re:jancyu2008]

jancyu2008

发贴: 36
积分: 0

于 2008-06-26 00:12

謝謝版主,我也想了一個解決的辦法,不過和你的相比顯得相形見拙了,呵呵,下面是我的辦法

public class Foo{
public static void main(String sgf[]){
  
  StringBuffer a = new StringBuffer("A");
  StringBuffer b = new StringBuffer("B");

  a.append(b);
  b=a;

  System.out.println(a+","+b);
}
}

jancyu2008 edited on 2008-06-28 00:05

Every day thinking about JAVA, because I like to
Welcome to My pagehttp://jeakylau.51.com
My E-mail:jeakylau@126.com
My QQ : 529163539

作者	Re:请教一个StringBuffer 问题!!!!!!!!!!!!! [Re:jancyu2008]
jancyu2008 发贴: 36 积分: 0	于 2008-06-26 00:26 今天又有了狠大的收獲

作者

Re:请教一个StringBuffer 问题!!!!!!!!!!!!! [Re:jancyu2008]

JiafanZhou

版主

发贴: 736
积分: 61

于 2008-06-27 16:19

jancyu2008 , there is a convention here people tend to adopt. i.e. put a code tag around the code snippet. Once you done that, the background of your code will look black, as to make others easy to read. Smile

Note there might be an issue from time to time if others edit your content. Hope it can be addressed soon.

Thanks,
Jiafan

When I was a kid I used to pray every night for a new bike. Then I realized that The Lord doesn't work that way, so I stole one and asked him to forgive me.

作者	Re:请教一个StringBuffer 问题!!!!!!!!!!!!! [Re:jancyu2008]
jancyu2008 发贴: 36 积分: 0	于 2008-06-28 00:09 Ah ,I don't know what can I do it on the frist Hehe ,thank you Every day thinking about JAVA, because I like to Welcome to My pagehttp://jeakylau.51.com My E-mail:jeakylau@126.com My QQ : 529163539

作者

Re:请教一个StringBuffer 问题!!!!!!!!!!!!! [Re:HenryShanley]

Joffeec

发贴: 47
积分: 3

于 2008-06-29 11:25

HenryShanley wrote:

> 输入的结果如何才能变成AB,AB

x.append( y );
y.delete(0, y.length());
y.append(x.toString());

版主可以用一个y.delete(0,y.length());先来删掉y里面的内容再用append()的方法把x的内容加进去。。那么我用一个replace()也可以达到同样的效果。


 x.append( y );
 y.replace(0,1,x.toString());

Joffeec edited on 2008-06-29 11:27

作者

Re:请教一个StringBuffer 问题!!!!!!!!!!!!! [Re:Joffeec]

jancyu2008

发贴: 36
积分: 0

于 2008-06-29 23:45

Joffeec wrote:
版主可以用一个y.delete(0,y.length());先来删掉y里面的内容再用append()的方法把x的内容加进去。。那么我用一个replace()也可以达到同样的效果。

x.append( y );
y.replace(0,1,x.toString());

Yes , Hehe ,thanks

Every day thinking about JAVA, because I like to
Welcome to My pagehttp://jeakylau.51.com
My E-mail:jeakylau@126.com
My QQ : 529163539

作者	Re:请教一个StringBuffer 问题!!!!!!!!!!!!! [Re:jancyu2008]
andy_wang_5 发贴: 101 积分: 14	于 2008-06-30 09:21 这是值传递和引用传递的问题鹰行折翼再盼凌云

作者	Re:请教一个StringBuffer 问题!!!!!!!!!!!!! [Re:andy_wang_5]
jancyu2008 发贴: 36 积分: 0	于 2008-06-30 23:03 andy_wang_5 wrote: 这是值传递和引用传递的问题 Of course. Java was very very hard ,but also very very easy Every day thinking about JAVA, because I like to Welcome to My pagehttp://jeakylau.51.com My E-mail:jeakylau@126.com My QQ : 529163539

作者

Re:请教一个StringBuffer 问题!!!!!!!!!!!!! [Re:jancyu2008]

jancyu2008

发贴: 36
积分: 0

于 2008-07-02 18:57

public class Foo
{public static void main(String[] sgf)
{   
 StringBuffer a = new StringBuffer("A"); 
 StringBuffer b = new StringBuffer("B");   
 operate(a,b);  
  System.out.println(a+","+b);//这里要求不能有变动
}
static void operate(StringBuffer x,StringBuffer y)
{   
   x.append(y);  
   y=new (x.toString());
}
}

这个也可以达到效果

Every day thinking about JAVA, because I like to
Welcome to My pagehttp://jeakylau.51.com
My E-mail:jeakylau@126.com
My QQ : 529163539

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