uninitialized local variables.

[srikanth bhadragiri]

Trying to retrieve values from uninitialized local variables throw compiler error.

The below code snippet throw compiler error for usage of 'price' in SOP. This is fine.

-------------------- Code Snippet ------------------------------

public static void main(String[] args){

int price;

if(Boolean.TRUE){
price = 100;
}

System.out.println(price);
}

---------------------------------------------------------------------------------
Replace
if(Boolean.TRUE){ .... }
with
if(true){ .... }
the code compiles and SOP displays 100 as output.

Q1) How is literal 'true' different from 'Boolean.TRUE' ?
Q2) How does the compiler treat 'true' and 'Boolean.TRUE' ?


Srikanth

[Jeanne Boyarsky]

Boolean.TRUE is an object and true is a primitive. Java takes care of autoboxing between the two for you.

[srikanth bhadragiri]

Jeanne Boyarsky wrote:Boolean.TRUE is an object and true is a primitive. Java takes care of autoboxing between the two for you.

Thanks for reply. I know about autoboxing in Java, but in this scenario replace if(Boolean.TRUE) with if(true). The result is different.

My question is why does compiler throw error in below first code snippet "if(Boolean.TRUE){}" and not in second code snippet "if(true){}"?
Is it something like autoboxing works only during runtime and not during compile time?

------------
// compiler throws error : price is not initialized
public static void main(String[] args){
int price;
if(Boolean.TRUE){ price = 100; }
System.out.println(price);
}
------------
// No compiler error
public static void main(String[] args){
int price;
if(true){ price = 100; }
System.out.println(price);
}

[Henry Wong]

srikanth bhadragiri wrote:

Jeanne Boyarsky wrote:Boolean.TRUE is an object and true is a primitive. Java takes care of autoboxing between the two for you.

Thanks for reply. I know about autoboxing in Java, but in this scenario replace if(Boolean.TRUE) with if(true). The result is different.

My question is why does compiler throw error in below first code snippet "if(Boolean.TRUE){}" and not in second code snippet "if(true){}"?
Is it something like autoboxing works only during runtime and not during compile time?

------------

// compiler throws error : price is not initialized
public static void main(String[] args){ 
int price; 
if(Boolean.TRUE){ price = 100; } 
System.out.println(price); 
} 

------------

// No compiler error
public static void main(String[] args){ 
int price; 
if(true){ price = 100; } 
System.out.println(price); 
}

A boolean true literal is a compile time constant. A Boolean.TRUE, actually any Boolean instance, is *not* a compile time constant. In the second case, the compiler is able to determine that the condition will always run. And in the second case, the compiler is not able to make the same determination, hence, can't determined that it is guaranteed to be executed.

Henry