Why doesn't this compile?
JAVA5 is a static final boolean.
I get a cannot find symbol result, shouldn't the compiler determine the result of the if statment, and act as though it weren't there?
How can I modify it to do what I want it to, i.e. compile with StringBuilder if JAVA5 is true.
public String toString(){
if(JAVA5){
StringBuilder result = new StringBuilder(1000);
}else{
StringBuffer result = new StringBuffer(1000);
}
for(int[] i : matrix){
for(int j : i){
result.append(j);
}
result.append('\n');
}
}
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>>shouldn't the compiler determine the result of the if statment, and act as though it weren't there?
No - if the symbol 'JAVA5' can't be resolved then you're in trouble. Even if it could be, you can't do what you're trying to do:
>>How can I modify it to do what I want it to, i.e. compile with StringBuilder if JAVA5 is true.
Once you've fixed that, the only way i know of doing this in the compilation unit is to use reflection:
final boolean JAVA5 = (System.getProperty("java.
Object stringThing = null;
if (JAVA5) {
Class clazz = Class.forName("java.lang.S
stringThing = clazz.newInstance();
}
}
No problems with the JAVA5 variable, the cannot resolve symbol was related to the variable result. Sorry I should have made that clearer.
petmagdy the problem with your code is that StringBuffer can't be assigned to a StringBuilder.
StringBuilder result =null;
if(JAVA5){
result = new StringBuilder(1000);
}else{
result = new StringBuffer(1000);
However, using an Object wouldn't work either because I need to cast to the appropriate class to do so, and I wouldn't know which class to cast to.
the reason is local variables "StringBuilder result" must be assured to be declared and intialized before usage this assurance can't be code sections like if, while, etc
But it can be assured, result will be either one or the other, and the type of which can be determined at compliation time. But indeed the compiler doesn't seem to agree, so how else can I do it. Really need something in the form of a #ifdef statment in c.
If I remember correctly, the procedure is as follows:
1) Analyze your requirements from both classes; StringBuilder and StringBuffer.
2) Create an interface or abstract class that declares the unified functionality of both classes.
3) Write two implementation classes that implement the interface/abstract-class you did in phase #2. Each implementation class uses its proper counterpart.
4) Rewrite the method that looks for JAVA5 to load and initialize the proper wrapper based on whether JAVA5 is defined or not.
5) Rewrite any method that uses the StringBuffer/StringBuilder
I think that's it. Its quite a common architecture in pluggin-frameworks... and also how AWT works with Peer classes for different OS's.
I hope this helps :)
>>Really need something in the form of a #ifdef statment in c.
There isn't anything - that's the point of my answer. You can't declare variables of unsupported types as even if it doesn't fall over at compile time (e.g. you're using a 1.5 compiler) then it will fall over at load time on < 1.5 as the version will be unsupported by the vm.
You need a result of a < 1.5 binary and therefore you can't declare types >= 1.5, so you have to do it with reflection per my example
SaMuEl, you will notice that i stressed
>>the only way i know of doing this in the compilation unit
You can of course get preprocessing tools. Here's one although i have not tried it:
http://sourceforge.net/pro
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by: SaMuElPosted on 2005-02-05 at 13:52:12ID: 13235787
Oh, and before anyone says it, I know the for each loop doesn't exist prior to Java 5, and I realise my toString method isn't returning anything. However, that's not the point.