Develop Reference

Android compile single .java file to .class

I have same jar lib for android where I need change class. I opened .jar find and decompile class, do same changes. I need add updated file to jar. As I understand I need compile .java to .class, and then repack jar.
I try convert to classes with javac.exe MyClass.java and I get a lot of errors like
import android.annotation.SuppressLint;
.java:8: error: package android.content does not exist
import android.content.Context;
.java:9: error: package android.graphics does not exist
import android.graphics.Color;
in total 149 errors
Do you have any ideas?

These error messages are the java compiler telling you that there's some android dependencies that he can't figure out how or where to find.
I don't think it's possible to achieve this, because it seems your class relies on Android framework resources.
Take a look at:
compile android app with javac
Did you consider inheritance ? I mean, the desired different behaviour for android maybe can be achieved by inheriting the class then overriding the specific method with new behaviour, I'm just guessing, since I don't have enough info about your problem.

Importing a JAVA package doesn't exist

I am having a problem with a Java Class which keeps saying me the package I am trying to import doesn't exist but as you can see the package exist. The package name is SecuGen and it exist in the folder.

check your classpath in your IDE.
do a clean and build

How to search unresolved libraries in Intellij IDEA or Android Studio?

I'm trying to port Apache Flink to Android. One of the biggest problem is that some java tools doesn't exist for Android, but these conflict are not detected at compile time and the errors (NoClassDefFoundError excpetion) are detected only at runtime.
For example, Java's ManagementFactory doesn't exists for android, BUT no compile error is thrown even if in this class there are unresolved symbols/libraries, in particular:
import javax.management.MBeanServer;
import java.lang.management.BufferPoolMXBean;
import java.lang.management.GarbageCollectorMXBean;
import java.lang.management.ManagementFactory;
import java.lang.management.MemoryMXBean;
import java.lang.management.MemoryPoolMXBean;
import java.lang.management.MemoryType;
import java.lang.management.MemoryUsage;
Now, I included the Flink's jars (flink-clients, flink-java, flink-runtime and flink-streaming) in my Android Studio project and I would like to search all these kind of unresolved dependencies to avoid these kind of exception at runtime. There is any Android Studio tool for this purpose?

I think including jar dependencies in the project will not make Android Studio and a compiler to search for missing classes in already built jars. Try to include src of flink into your project. I tried that and I had all unresolved imports being red.

Java library import difficulty

I'm trying to compile a small test program I have written for a raspberry pi.
The program makes use of the Pi4J library to control the piface add-on board.
What I have done so far is based on the following tutorial: http://www.savagehomeautomation.com/piface
While I can get the above example program to compile within my IDE after setting up the class paths I get compile errors with the one I have made and as far as I can tell the imports are set up in the same way.
It says that each of the following packages does not exist:
import java.io.IOException;
import com.pi4j.component.switches.SwitchListener;
import com.pi4j.component.switches.SwitchState;
import com.pi4j.component.switches.SwitchStateChangeEvent;
import com.pi4j.device.piface.PiFace;
import com.pi4j.device.piface.PiFaceLed;
import com.pi4j.device.piface.PiFaceRelay;
import com.pi4j.device.piface.PiFaceSwitch;
import com.pi4j.device.piface.impl.PiFaceDevice;
import com.pi4j.wiringpi.Spi;
I'm assuming that my problem is relatively simple but I don't really understand how import statements work and it's quite vague topic to search about. I have included some file paths if that helps.
This is where my project resides:
/home/pi/JBerries/relay
and this is where the pi4j library is:
/opt/pi4j
I hope the following image provides some of the information requested, note that the class paths are already set up:

You need to set the CLASSPATH environment variable to /opt/pi4j or the jar file therein. WIthout this the compiler is unable to know where your libary is located and will give you the errors you describe.

If you're using a project in JBerries you need to configure the classpath for the project - the screenshot shows the classpath for single-file compilations only. To edit the project config right-click the root node in the project window and select properties.

error package org.python.util does not exist, compilation with ant

I am trying to call a python method in java, similar functionality as Unresolved import org.python / working with jython and java?
However, I am using ant to compile and run my files. using import org.python.util will give me this error
package org.python.util does not exist
I can see that python.org.util exists in jython-2.5.0.jar.
So, here is the class path I have in my build.xml ant file:
classpath="${java.class.path}:./jgrapht/lib/jgrapht-jdk1.5.jar:\
./jgrapht/lib/jgraph.jar:./jgraphx/lib/jgraphx.jar:\
./jython/lib/jython-2.5.0.jar:./colt/lib/colt.jar:."
and I also I added the path to jython jar files to my class path. i.e. looks like echo $path gives me all the required paths. Is there anything missing here that I am not aware of?

Try this to make all classes in the package available:
import org.python.util.*;
Or this to include a particular class:
import org.python.util.TemplateAntTask;
EDIT: Also, looks like there is an extra slash after jython-2.5.0.jar in your classpath.