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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

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
Maciej
Do somebody tell me a best nano engineering book for beginners?
s. Reply
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
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.
Tarell
what is the actual application of fullerenes nowadays?
Damian
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.
Tarell
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.
Virgil
is Bucky paper clear?
CYNTHIA
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.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
AMJAD
what is system testing
AMJAD
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
Hello
Uday
I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
can nanotechnology change the direction of the face of the world
Prasenjit Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit 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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