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Jiris Mock 1, Q1

 
Ranch Hand
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Why does this code throw an exception at runtime?
 
mister krabs
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Originally posted by Cathy Song:
Why does this code throw an exception at runtime?

Ultimately this null String gets passed into the write method of Writer which assumes that the String is not null. It runs the getChars method of the String which is where the exception occurs. Again, this is another case where reading through the source and following the stack trace can help you understand the API better.
 
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Originally posted by Cathy Song:

Why does this code throw an exception at runtime?


hello,
I suppose that the return type String is expected and null is returned if we return "null" it works - no runtime exception is thrown.
just make few changes in toString method and it works....
public String toString(){
if(i==0)
return "null";
else
return ""+i;
}
pls correct me am wrong....
 
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The following code did not throw any exception for me and the output was 2 and null.
I compiled with jdk1.4
class Class2
{
int i;
public Class2(int i) { this.i = i; }
public String toString()
{
if(i == 0) return null;
else return ""+i;
}
public static void main(String[ ] args)
{
Class2 t1 = new Class2(0);
Class2 t2 = new Class2(2);
System.out.println(t2);
System.out.println(""+t1);
}
}
Any thoughts?
 
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This is a known JVM bug ID=4339222 (Synopsis: System.out.println throws NullPointerException when toString() returns null).
Workaround: Subclass and override toString, avoid to System.out.println.
Login to Bug Database for a full description.
 
Greenhorn
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Hi,
Following expression works as well.
public String toString()
{
if(i == 0)
return "" + null;
else
return "" + i;
}

Thanks,
PJ
 
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But explicitly calling "toString()" method works (jdk1.4). Wierd.
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