class Test {
public static void main(String args[])
{
Boolean expr = true;
if (expr)
{
System.out.println("true");
}
else
{
System.out.println("false");
}
}
}
EDIT:
the error is java.lang.UnsupportedClassVersionError
Static should be with lower case: static.
Check this link
java.lang.UnsupportedClassVersionError: why is it thrown & how to resolve?
How to resolve UnsupportedClassVersionError?
Whenever you encounter this error, do check if you’re using an earlier
version of JVM to execute the class file than the corresponding
version of compiler you used to compile the source code. The example
shown here was compiled using Java 5.0 compiler, but when I tried to
run using JVM 1.4, I got the above error. I just needed to switch
either to a JVM version 5.0 or above OR needed to switch to a Java
Compiler of JDK 1.4 or below (you of course need to make sure the
source code is compatible with the corresponding version of the
compiler otherwise you’ll start getting other compiler errors).
A higher JVM version doesn’t cause a problem in most of cases unless
the class file format is quite old (and hence doesn’t lie in the
supported range as specified by Sun for that particular JVM version
... as discussed above). But, it’s always a good practice to have both
the Compiler and the JVM of the same version.
This is no runtime error. This doesn't compile.
Use static (lowercase s) instead of Static.
static should be lower case, and I believe you need it to be a public class. Also why are you using Boolean instead of boolean, wrapper types aren't necessary here.
This code (if using JDK 5 and upwards, because of autoboxing/unboxing) runs perfectly without any RuntimeException and it will display true on the console.
I think you are compiling with one version of java and running with another. To be clearer you are compiling with a later version of java and running with an earlier version.
Are you compiling and running this class in an IDE?
Related
Hi I am writing a Java class that enables some of its functionalities when it is compiled with java7 upwards.
I know how to find the major/minor magic number from a compiled class file. But I need to find a way to detect that when the compiler is compiling my source code.
A simple snippet for this:
```
public class Hey
{
public static final boolean JAVA_VER = ???; // how to do this??
public static foo() {
if (JAVA_VER >= JAVA7) {
// use the fancy way introduced in java7
} else {
// go with the slow way of java6
}
}
}
```
Code is not executed during compilation. During compilation it is checked for syntactical errors and converted to byte code inside a .class file. Code lines can be executed when it is run and hence the only thing you can find out in your code is java runtime version. Java runtime can be found using java.version system property. Here is the code for that:
String version = System.getProperty("java.version");
If you want to check the java compiler version, perhaps then you use a script to compile your code. Maybe you can have two different versions of your file, each one apt for one particular java version. In your script check the available java version and compile the desired version of file. You may want to use single output common output directory.
This should be impossible. The compiler requires that the JVM running the code have the same version as the code being run - in essence, you cannot compile that for a lower version because the higher version code needs a higher version compiler.
In the case you were able to get around this, I would probably pack a script as mentioned before, or programmatically do so in a bootstrap by executing a byte code dump (which specified the major/minor version) either with Process or source decoding from the File bytes.
As far as i know, during the compile time of Java, only the class/method signatures are recorded. The actual implementations are binded until the running time, in the JVM.
Let's imagine there is a native Java class called MyClass. And in Java version 1.6:
public class NativeClass {
public String getVersion() { return "1.6"; }
}
And in Java version 1.7:
public class NativeClass {
public String getVersion() { return "1.7"; }
public String somethingMore() { return "more"; }
}
Our IDE and compiler are 1.7. After the program compiled, when we run it in JRE 1.6 and 1.7, we will have different return values from NativeClass.getVersion();. This is known.
But what will happen if we run NativeClass.somethingMore() on JRE 1.6?
If possible, please give an example in the real Java source, where certain class/method only exist in a newer version.
But what will happen if we run NativeClass.somethingMore() on JRE 1.6?
A NoSuchMethodError will be thrown.
Thrown if an application tries to call a specified method of a class (either static or instance), and that class no longer has a definition of that method.
What if a class that doesn't exist? There is no NoSuchClassError
See NoClassDefFoundError & ClassNotFoundException.
But don't ask me a) why there are two of them. b) why one is used over the other/what the difference is, or c) why methods also have NoSuchMethodException.
It seems they should all be an Error rather than an Exception.
Andrew Thomson is correct as far as he goes. Here's a more fulsome answer:
The first point is that if you compile code using a Java 1.7 SDK (or IDE), and try to run it on Java 1.6 (or earlier), you may run into a "magic number" error. Basically, unless the "target version" is set to the older version, the compiler will emit bytecode files that the older JVM cannot understand.
Once you have gotten past that:
Attempting to call a method that doesn't exist will result in a NoSuchMethodError.
Attempting to use (in any way) a class that doesn't exist will result in a ClassDefNotFoundError.
The errors are detected and thrown at the point when the JVM tries to resolve the dependencies between the classes. (This is referred as "linking" in the JLS. It happens some time before the class is "initialized", but the JVM is free to implement loading and linking lazily so it might not happen instantly on application startup.
Both of these are fatal errors. They leave the JVM in a state where the application is unlikely to be able to recover because an indeterminate set of the application's essential classes are not usable.
These are examples of "binary compatibility errors". Other examples include things like missing fields, methods with the wrong signatures, some changes in access modifiers, changes to the inheritance hierarchy, and so on. (There is a whole JLS chapter that deals with the binary compatibility rules; i.e. what you can and can't change in a class without breaking compatibility.)
This is all common sense really. If you attempt to call a method that isn't there or use a class that isn't there, bailing out with a fatal error is the only safe thing to do. There are practical limits to "write once, run anywhere".
If you want a simple example, try running an application that uses String.isEmpty() on a Java 1.5 or earlier JVM. (Or an early release Android phone ...)
You won't get a ClassNotFoundException. That is only thrown when you attempt to load classes using Class.forName(...).
This code works well with the latest MySQL JDBC driver - mysql-connector-5.1.22
Connection conn = DriverManager.getConnection"jdbc:mysql://localhost:3306/test", "root", "root");
conn.getSchema();
but if I use an older version, eg mysql-connector-5.1.20 I'll get
Exception in thread "main" java.lang.AbstractMethodError: com.mysql.jdbc.JDBC4Connection.getSchema()Ljava/lang/String;
at main.MySQL.main(MySQL.java:21)
because Connection.getSchema is since 1.7.
If a concrete class is missing, eg. Integer.compare(int, int) is since 1.7 you'll get java.lang.NoSuchMethodError
If a JRE class was missing, e.g. java.util.Scanner is since 1.5 and I used JRE 1.4 I would get java.lang.NoClassDefFoundError
I have dowloades the sources of the android musicplayer vanilla. When i compile it with eclipse i get several compiler-error
that complain that a method with #Override is not an override.
I made the source compilable by removing the false #Overrides.
I donot know, why there are these wrong #Overrides.
Maybe they are there because the autor developed for an other android-baseclasslibrary that has these methods while my
java 6 with android 2.1 does not have it.
Is there a way to make it compileable without deleting the false #Overrides?
You need to switch to JDK6 :
Enable Java 1.6 Compiler in your project properties under Java Compiler
Make sure your java Runtime Environement is at 1.6
The problem may come from using different versions.
It's not a good practice to make it compileable without deleting the false #Overrides because it is made for a reason and if you CAN disable it, you may have problems elsewhere and you wouldn't know where the problems are happening
So, just delete the false or check for a newer version of vanilla
I know, this sounds like an old question, which has been asked before(*). But it is a little bit different. I installed a clean system with the newest versions of JDK (7u2) and eclipse (and also AndroidSDK). When I import old projects, I get an error "The method methodName(Parameter) of type Class must override a superclass method".
The #override-tag was there (correctly), because the method overrides a method of an INTERFACE of the superclass. somehow compiler thinks that this tag is just for superclass directly. As far as i know #override is not changed in Java 7 and my project was working properly on 6. Is it a possible bug or compability problem or I am missing something?
(*)Similar problem used to happen, when compiling on JDK5, simply because #override was yet implemented in Java 5. Solution was, of course changing compiler compliance level to 6. But what is it with JDK 7 now?
You shouldn't use JDK 7 for the development. There is a requirement that you have to use JDK 5 or 6.
I have implemented successfully the reflectionEquals method, with a list of excluded fields.
return EqualsBuilder.reflectionEquals(this, obj, new String[] {"files", "notes", "status"});
However, I recently compiled my program on Java 1.5 and now I get the following error when the program hits the above line:
java.lang.NoSuchMethodError:
org.apache.commons.lang.builder.EqualsBuilder.=
reflectionEquals(Ljava/lang/Object;Ljava/lang/Object;[Ljava/lang/String;)Z
If anyone has an insight on why the method does not exist at runtime, I would appreciate it
Every NoSuchMethodError that I've ever encountered has (eventually) been found to be a mismatch between the version of an external library on the classpath at compile time vs. the version of the library on the classpath at runtime (i.e. - in this case, you would have a different version of apache commons on your classpath when the application is compiled than when it is running.)
The method was definitely there when your code was compiled - or a compiler error would've been thrown.
Check the versions of commons-lang.jar on your classpaths - I'm betting you'll find a mismatch.
It's worth noting that this is NOT a MISSING jar file - that would throw a ClassNotFoundException (maybe eventually followed by a NoClassDefFoundError.)
This is likely a var args problem. Be sure to recompile everything in java 1.5 and be sure you are running it on java 1.5, and be sure you reference the same jar at compilation as at runtime.
You may have an older version on your runtime classpath.
Get the latest version of Apache Commons Lang