I know I'm throwing a pretty stupid question, but I promise I did try to search around the settings and around google and the webs and no luck, so I guess I should just ask.
I saw in quite a few open-source projects the following line:
if(DEBUG){
// do some logging
}
I perfectly understand what the line is doing, I just can't seem to repeat it.
There's no declaration of boolean DEBUG; anywhere in the code, and I couldn't figure out a place on the project properties to define a system wide variable to be replaced on the compiling (into byte code). And as far as I know, if it's a reference to a class constant it was supposed to be Log.DEBUG or something similar.
Can anyone solve this mystery for me?
thanks.
You really should look at the import section of the class.
It is probably a static import, like this :
A.java
public class A {
public static boolean DEBUG = false;
}
B.java
import static A.DEBUG;
public class B {
public void myMethod() {
if (DEBUG) {
// do something
}
}
}
You are in front of a public static field, look in import list and pick the original class or, use the inline help from Eclipse as said in comments
Related
I have looked through many answers to similar questions. But couldn't narrow down to a solution.
Following is the code: (Simplifying names for readability)
First class:
package p1;
public class C1 {
public static void test() {
System.out.println("Boom!");
}
}
Second class:
package p2;
import p1;
public class C2 {
public static void main(String[] params) {
C1.test();
}
}
Clean-Build doesn't give any error. (No compilation error)
But at runtime I'm getting following error:
Exception in thread "main" java.lang.NoSuchMethodError: C1.test()V
at C2.main(C2.java:6)
Java Result: 1
P.S. I'm using Netbeans.
This means that you are running your class C2 with an old version of class C1 in the classpath (a version that did not yet have the test() method).
Make sure you don't have old versions of C1.class somewhere. Remove all your *.class files and recompile everything, and then try to run it again.
Addition: As Kevin Bowersox noted in a comment, your main method must look like this:
public static void main(String[] args)
It must take a String[] as an argument.
It will properly compile and run only if main function will have String tab as args.
But also check versions of class C1 and C2, try rebuild your project to recompile that classes.
public static void main(String args[]) {
C1.test();
}
i think you should import it as
import p1.*;
Than you will get access to all classes and member functions in it.
Netbeans sometimes likes to get stuck after some changes and clean build doesn't work then.
Try editing each file that has been recently modified and saving it again (e.g. put a whitespace in a random place). After that, clean and build the project again.
If my memory refreshes and as Jesper pointed out, I also encountered that same issue NoSuchMethodFoundException under that same scenario (having still old class references that have not been cleaned).
I just copied your code snippets with 2 different packages directly in to my netbean, compiled and runned C2. It did print the BOOM! message.
In my case using :
public static void main(String args[]){
}
does not make a difference when I compiled and runned the code.
public static void main(String params[]){
}
It makes sense since the main class should have the correct method signature of main.
Here args or params, should not make a huge difference, I believe; as what we have inside the method is simply a reference for the inner body of the method that it uses.
Still definitely it is good practice to follow the standard signature for main.
I would recommend to clean the project and copy the contents from scratch in a new project and build it again, sometimes netbeans can go crazy.
I know what static is.. Globally.
So I was looking through a code, to get better in coding myself. I'm looking through the Minecraft source code, and for those who are interested to look there its in the files "TileEntity.java" and "EntityList.java". It is definitely not necessary to look over there, because its just a manner of programming.
So, we have just your regular class with a method:
public class EntityList{
public static void addMapping( /* variables that dont matter */ ){
//Call other methods, also unimportant
}
}
After that there is a class that imported EntityList and does this:
import the.path.to.EntityList;
public class TileEntity{
static{
addMapping( /* vars */ );
addMapping( /* vars */ );
}
}
Now I'm wondering: How does this work? Please let me know if you need to know more background of the code, but I cannot redistribute the file due to copyright and stuff. Then you have to decompile Minecraft if you have it yourself.
We can't see the real code, but my guess is that it contains a static import:
import static the.path.to.EntityList.addMapping;
or
import static the.path.to.EntityList.*;
A static import allows referring to a static field or method of a class without having to type the name of the class.
See http://docs.oracle.com/javase/1.5.0/docs/guide/language/static-import.html for more details.
Im trying to use Scala and Java in one project. Im working with the Scla IDE for Eclipse. I have two packages in my Scala Project: one for my scala code and one for my java code.
Now lets say I create new JavaClass with one static member.
package javastuff;
public class MyJavaClass {
public static String MESSAGE = "Im Java";
}
After that Im trying to get access to this variale and somehow I cannot. Funny thing, because scala is able to see the Java class "MyJavaClass" just not able to see MESSAGE.
import javastuff.MyJavaClass
object Main {
def main(args: Array[String]) {
println(MyJavaClass.MESSAGE)
}
}
Value MESSAGE is not a member of object javastuff.MyJavaClass
If I use Project/Clean... 1-2x times eclipse is maybe starting realizing that the member MESSAGE is really there and everything is fine. Is this normal? Maybe Im doing something wrong, I know eclipse is really a bad IDE and I should maybe try IntelliJ, but somehow I like eclipse and I would like to use later some of my favorite plugins, thats why I would not change the IDE just because of this problem. Any ideas how to handle this problem better?
Scala doesn't have any static fields. Here is a blogpost about it
btw. public static without final is pretty bad design (no encapsulation => possible memory leaks)
I love the Intellij IDEA but i have been stacked on one little problem with Java imports.
So for example there is a package with name "example" and two different classes in it: A.java and B.java.
And i wanna get access to class "A" from class "B" without imports. Like this:
class A:
package example;
public class A{ ... some stuff here ...}
class B:
package example;
public class B{
public static void main(String[] args){
A myVar = new A();
}
}
This code may not work, but it's doesn't matter. Trouble just with IDE and with its mechanism of importing classes.
So, problem is that i can't see A class from B. Idea says 'Cant resolve symbol' but i actually know that class A exists in package. Next strange is that complier works fine and there are no exceptions. Just IDEA can't see the class in the same package.
Does anybody has any ideas?
If they are in the same package, you can access A in class B without import:
package example;
public class B{
public static void main(String[] args){
A myA = new A();
}
}
Maybe this will help you, or somebody else using IntelliJ that is getting a "Cannot resolve symbol" error but can still compile their code.
Lets say you have the two files that buymypies wrote up, the standard Java convention is that the two files would exist in an Example directory in your source code area, like /myprojectpath/src/Example. But it is technically not a requirement to reflect the package structure in the source directory structure, just a best practice sort of thing.
So, if you don't mimic the package structure, and the two files are just in /myprojectpath/src, IntelliJ will give you the "Cannot resolve symbol" error because it expects the source code structure to reflect the package structure, but it will compile okay.
I'm not sure if this is your problem, but I do use IntelliJ and have seen this, so it's something to look at.
I have the same problem as this: 2 classes in the same package, yet when one tries to call the other, Intellij underlines it in red and says Cannot resolve symbol 'Classname', e.g. Cannot resolve symbol 'LocalPreferencesStore'.
It then wants to add the fully qualified name in situ - so it clearly knows the path - so why can't it just access the class?
The module still compiles and runs, so it's just the IDE behaving oddly - and all that red is very distracting, since it isn't actually an error, it's just IDEA throwing a weird wobbly.
This is also recent. Two weeks ago I wasn't having this problem at all, and now suddenly it's started up. Of course, it could go away again on its own soon, but it's really annoying.
Same issue and I just fixed it.
I don't know your folder structure.
However, if your package example was added manually.That's the problem.
The package should be the same as your folder structure,which means if you want your class file to be stored in package example,you must store you java file in the src's subfolder named example.
You need to learn the basics about Java i think.
Here is a basic example of what i think you are trying:
package Example;
public class A
{
String myVar;
public String getMyVar()
{
return myVar;
}
public void setMyVar(String myVar)
{
this.myVar = myVar;
}
}
You need to create an instance of A.
package Example;
public class B
{
/**
* #param args
*/
public static void main(String[] args)
{
// TODO Auto-generated method stub
A myA = new A();
myA.setMyVar("Hello World!");
System.out.println(myA.getMyVar);
}
}
Look up java 'getters' and 'setters'.
So, I have something written in Java, and I want to extend it in Scala... The issue I'm running into is that Scala isn't seeing methods I need.
Here is how it's set up:
Player extends Mob, and Mob extends Entity.
I need to access a method in Player that isn't defined in Mob or Entity, but Scala doesn't think it exists even though Java does.
It can see methods defined by Mob and Entity just fine. Also, all the methods I'm talking about are non-static.
So, am I doing something wrong, or is this a limitation imposed by Scala?
Edit --
Here is the relevant code:
package test
import rsca.gs.model.Player
object Test {
def handle(p:Player): Unit = {
p.getActionSender().sendTeleBubble(0, 0, false);
}
}
Player class:
package rsca.gs.model;
// imports
public final class Player extends Mob {
// Implemented methods (not going to post them, as there are quite a few)
// Relevant code
private MiscPacketBuilder actionSender;
public MiscPacketBuilder getActionSender() {
return actionSender;
}
}
Error:
value getActionSender is not a member of rsca.gs.model.Player
I never encountered such problems, and you probably checked your configuration and everything else twice, so I would guess this is some Eclipse related build issue. You should try to build from the command line in order to see whether Scala or Eclipse is the problem.
Is it possible for you to run a test against the class just to see if you got the right one?
p.getClass.getMethods
... and if possible (may run into NPE) in order to find the source:
p.getClass.getProtectionDomain.getCodeSource.getLocation.getPath
When compiling the Scala class, do something like this:
scalac *.scala *.java
This way, Scala will look a the Java code to see what is available. If, however, the Java code is already compiled and provided as a jar file, just add it to the classpath used when compiling the Scala code.