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A Java program can be syntactically correct but still not compile because of errors related to the semantics of the language.

This group of errors results from code that is syntactically correct but violates the semantics of Java, in particular the rules relating to type checking.

variable ... might not have been initialized

An instance variable declared in a class has a default initial value. A class is a template that is used to create or instantiate instances called objects . Since memory is allocated separately for each object, these variables are called instance variables . However, a local variable declared within a method does not, so you are required to initialize it before use, either in its declaration or in anassignment statement:

void m(int n) {   // n is initialized from the actual parameter   int i, j;  i = 2;             // i is initialized by the assignment   int k = 1;         // k is initialized in its declaration  if (i == n)        // OK     k = j;           // Error, j is not initialized  else     j = k;}

The variable must be initialized on every path from declaration to use even if the semantics of the program ensure that the path cannot be taken:

void m(int n) {   int i;  if (n == n)           // Always true     i = n;  else     n = i;              // Error, although never executed!!}

Eclipse: The local variable ... may not have been initialized

Note: If the expression in the if -statement can be computed at compile-time:

if (true)                  // OK if ('n' == 'n')            // OK

the error will not occur.

... in ... cannot be applied to ...

This error message is very common and results from an incompatibility between a method call and the method's declaration:

void m(int i) { ... }  m(5.5);        // Error, the literal is of type double, not int

Check the declaration and call carefully. You can also get the error message cannot find symbol if the declaration of the method is in the API. The Application Programming Interface (API) describes how to use the library of classes supplied as part of the Java system. Byextension, it is also used as a name for the library itself.

Eclipse: The method ... in the type ... is not applicable for the arguments ...

operator ... cannot be applied to ...,...

Operators are only defined for certain types, although implicit type conversion is allowed between certain numeric types:

int a = 5; boolean b = true;int c = a + b;       // Error, can't add a boolean value double d = a + 1.4;  // OK, int is implicitly converted to double

Eclipse: The operator + is undefined for the argument type(s) int, boolean

possible loss of precision

This error arises when trying to assign a value of higher precision to a variable of lower precision without anexplicit type cast. Surprisingly, perhaps, floating point literals are of type double and you will get this message if you try to assign one to a variable of type float :

float sum = 0.0;          // Error, literal is not of type float

The correct way to do this is to use a literal of type float or an explicit type cast:

float sum = 0.0f;         // OK float sum = (float) 0.0;  // OK

Eclipse: Type mismatch: cannot convert from double to float

incompatible types

Java checks that the type of an expression is compatible with the type of the variable in an assignment statement and this error will result ifthey are incompatible:

boolean b = true; int a = b;              // Error, can't assign boolean to int

Eclipse: Type mismatch: cannot convert from boolean to int

Important note
In the C language it is (unfortunately!) legal to write if (a = b) using the assignment operator instead of if (a == b) using the equality operator. The meaning is to execute the assignment, convert the value to an integerand use its value to make the decision for the if -statement (zero is false and non-zero is true). In Java, the assignment is legal and results in a value,but (unless a is of type boolean !) this error message will result because the expression in an if -statement must be of type boolean , not int . Writing == instead of = becomes a simple compile-time error in Java, whereas in C this error leads to runtime errors that are extremelydifficult to find.

inconvertible types

Not every type conversion is legal:

boolean b = true; int x = (int) b;   // Error, can't convert boolean to int

Eclipse: Type mismatch: cannot convert from ... to ...

Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
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Source:  OpenStax, Compile and runtime errors in java. OpenStax CNX. Dec 28, 2009 Download for free at http://cnx.org/content/col10913/1.2
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