Java: Why am I required to initialize a primitive local variable?
In fact, the compiler does not assign a default value to your float f
, because in this case it is a local variable -- and not a field:
Local variables are slightly different; the compiler never assigns a default value to an uninitialized local variable. If you cannot initialize your local variable where it is declared, make sure to assign it a value before you attempt to use it. Accessing an uninitialized local variable will result in a compile-time error.
Because it's a local variable. This is why nothing is assigned to it :
Local variables are slightly different; the compiler never assigns a default value to an uninitialized local variable. If you cannot initialize your local variable where it is declared, make sure to assign it a value before you attempt to use it. Accessing an uninitialized local variable will result in a compile-time error.
Edit: Why does Java raise this compilation error ?
If we look at the IdentifierExpression.java
class file, we will find this block :
...
if (field.isLocal()) {
LocalMember local = (LocalMember)field;
if (local.scopeNumber < ctx.frameNumber && !local.isFinal()) {
env.error(where, "invalid.uplevel", id);
}
if (!vset.testVar(local.number)) {
env.error(where, "var.not.initialized", id);
vset.addVar(local.number);
}
local.readcount++;
}
...
As stated (if (!vset.testVar(local.number)) {
), the JDK checks (with testVar
) if the variable is assigned (Vset
's source code where we can find testVar
code). If not, it raises the error var.not.initialized
from a properties file :
...
javac.err.var.not.initialized=\
Variable {0} may not have been initialized.
...
Source
Actually local variables are stored in stack.Hence there is a chance of taking any old value present for the local variable.It is a big challenge for security reason..Hence java says you have to initialise a local varible before use.
Class fields (non-final
ones anyway) are initialized to default values. Local variables are not.
It's not always necessary to assign a value when a field is declared. Fields that are declared but not initialized will be set to a reasonable default by the compiler.
So a (non-final
) field like f
in
class C {
float f;
}
will be initialized to 0f
but the local variable f
in
void myMethod() {
float f;
}
will not be.
Local variables are treated differently from fields by the language. Local variables have a well-scoped lifetime, so any use before initialization is probably an error. Fields do not so the default initialization is often convenient.