Q: How can I run a simple Java application on my Android Emulator? I have some issues with connecting an external database on my Android Emulator. So, I thought I would try a simple Java program first. I compiled it using the "javac hello.java" command and then used the "javaw" command to execute the program. I got this: "Error: Could not find or load main class hello.hello" I believe that the error was because the program is looking for a class called hello and I gave it a class called hello.hello. Then, I tried compiling and executing with this command: "javac -d bin Hello.java" "java -d bin Hello" Here's what I get: "Error: Could not find or load main class Hello.Hello" I used the same code in the "javaw" command as I did with "javaw hello.hello". The first program I tried compiled and executed fine, but I want to run the second program (with the Hello.Hello class), because that's what my Java code is. I can post the source code, if you want, but I don't think it will be useful. Can you explain what I did wrong and what I can do to solve this problem? Thanks! PS: I am using Android Studio 2.2.1 and running in Windows 7 Home Premium. A: You are missing the name of your class if you give just a class name of your project and a jar file. javaw -cp "YOUR_JAR_PATH" Hello.Hello When you execute the program, if it is a simple java program, you should replace the parameter with Your class name and you must add the following at the end: java -cp "YOUR_JAR_PATH;." Hello.Hello If you want the method Hello to be called in your program, you should add public static void main(String[] args) at the top of your Hello class A: Your second error: Error: Could not find or load main class Hello.Hello is because you are not using the Hello.Hello class as the main class. When you use java -d bin Hello, your main class is Hello, which does not have a main method. You can change it by executing: javac -d bin Hello.java java -classpath bin Hello Make sure Hello.java is located in the bin directory. You might have other issues depending on what your code contains. A: If you are running from command prompt, java -cp "" ClassName The java program would look for the classname.class in your Java.jar file If you have other class dependencies, you can pass them like the following: java -cp java -cp ClassName Hope this is helpful. A: If you are running on Windows, you have to start command prompt with jdk_home\bin path or jdk_home\lib path (that is, you have to add -Djava.library.path=jdk_home\lib\ at the first command line before java Hello) Another solution is to add another command line : java -classpath ./lib -Djava.library.path=./lib Hello Note that if your application contains some .jar file that are from the outside the java_home, you must add their path in the first command line : java -classpath .\path_to_file.jar;.\path_to_another_file.jar ... If you need to add -cp ... on every program that you want to execute, you must specify the main class with -m parameter java -m Hello -cp "..\..\.." -Djava.library.path=.\lib Hello or java -m Hello -cp "..\..\.." Hello You can also use java -m Hello -cp .\lib Hello The program should be Hello.java EDIT (thanks @user163059) : The first case is needed in windows (sometime) because the lib folder has a sub-folder javaws.exe which would make the -classpath useless. EDIT2 : If you are not on Windows, you don't need the second argument in Windows ; if you are on Windows, this second argument is needed in Windows EDIT3 : In my system, I need also this property in JDK_HOME/jre/lib/security/java.security : permission java.lang.RuntimePermission "setIO"; and this property in \lib\jfxrt.jar : org.fife.ui.rs.RsFXApplication=com.sun.javafx.app.LauncherImpl