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Member initialization


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Trimite pe Messenger
Relational operators
Color, Font, Images, And Shapes
Introduction to Seam
Choice, Menus, And Checkboxes
The “visitor” pattern
Member initialization
Handling Text, Dialogs, And Lists
You never need to destroy an object
AWT Peer Interfaces
Coding style

Member initialization

Java goes out of its way to guarantee that any variable is properly initialized before it is used. In the case of variables that are defined locally to a method, this guarantee comes in the form of a compile-time error. So if you say:

void f()

You’ll get an error message that says that i might not have been initialized. Of course, the compiler could have given i a default value, but it’s more likely that this is a programmer error and a default value would have covered that up. Forcing the programmer to provide an initialization value is more likely to catch a bug

If a primitive is a data member of a class, however, things are a bit different. Since any method can initialize or use that data, it might not be practical to force the user to initialize it to its appropriate value before the data is used. However, it’s unsafe to leave it with a garbage value, so each primitive data member of a class is guaranteed to get an initial value. Those values can be seen here:


// Shows default initial values

class Measurement

public class InitialValues

The output of this program is:

Data type  Inital value

boolean  false


byte  0

short  0

int  0

long  0

float  0.0

double  0.0

The char value is a null, which doesn’t print.

You’ll see later that when you define an object handle inside a class without initializing it to a new object, that handle is given a value of null.

You can see that even though the values are not specified, they automatically get initialized. So at least there’s no threat of working with uninitialized variables.

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