How-to articles, tricks, and solutions about JAVA

To create an executable JAR with dependencies using Maven, you can use the maven-assembly-plugin. This plugin allows you to package your project and its dependencies into a single JAR file.

To print out all the elements of a List in Java, you can use a for loop or an enhanced for loop.

To change the date format in a Java string, you can use the SimpleDateFormat class.

To import a .cer certificate into a Java keystore, you can use the keytool utility that comes with the Java Development Kit (JDK). The keytool utility is a command-line tool that allows you to manage certificates and keystores.

Java does not have built-in support for default parameter values like some other programming languages.

To get the current working directory in Java, you can use the System.getProperty("user.dir") method. This method returns the current working directory of the Java process as a string. Here's an example:

The error javac is not recognized as an internal or external command, operable program or batch file occurs when you try to run the javac command from the command prompt, but the command prompt cannot find the javac executable.

The java.net.ConnectException: Connection refused exception is thrown when an application tries to connect to a remote host, but the connection is refused by the host. This can happen for several reasons, such as:

A NullPointerException is a runtime exception that is thrown when an application attempts to use an object reference that has a null value. To avoid this exception, you need to make sure that the object reference is not null before you use it.

The android.os.NetworkOnMainThreadException is a runtime exception that is thrown when an application attempts to perform a networking operation on the main thread.

To break out of nested loops in Java, you can use the break statement. The break statement terminates the innermost loop that it is contained in, and transfers control to the statement immediately following the loop.

To read a large text file line by line in Java, you can use a BufferedReader and pass it a FileReader object to read the file. Here's an example of how you can do this:

To check if a file exists in Java, you can use the exists method of the File class from the java.io package. This method returns true if the file exists, and false if it doesn't. Here's an example of how you can use this method:

There are several ways to copy an object in Java. Here are a few options:

To convert a file to a byte[] in Java, you can use the readAllBytes method of the Files class from the java.nio.file package. This method reads all the bytes from a file and returns them in a byte[]. Here's an example of how you can use this method:

To save a String to a text file in Java, you can use the write method of the FileWriter class. Here's an example of how you can do this:

To read all the files in a folder from Java, you can use the File class from the java.io package to list all the files in a directory. Here's an example of how you can do this:

To convert an ArrayList to a string in Java, you can use the join method of the String class, which allows you to join the elements of the ArrayList into a single string. Here's an example of how you might do this:

To get an enum value from a string value in Java, you can use the valueOf method of the enum type. Here's an example of how you might do this:

To add a local JAR file to a Maven project, you can use the maven-install-plugin. Here's how you can do it:

To get the current time in the YYYY-MM-DD HH:MI:Sec.Millisecond format in Java, you can use the SimpleDateFormat class and specify the desired format string:

This error message means that the Java compiler (javac) is not available in the current environment. This can happen if you are running a Java program from a Java Runtime Environment (JRE) rather than a Java Development Kit (JDK).

A "Cannot find symbol" or "Cannot resolve symbol" error in Java means that the compiler cannot find a symbol (such as a class, method, or variable) that it needs to complete the compilation. This can happen for a variety of reasons, including:

To run a JAR file on Windows, you will need to have the Java Runtime Environment (JRE) installed on your system. You can then run the JAR file by double-clicking it or by using the java command in the command prompt.

java.lang.NoClassDefFoundError is an error that occurs when the Java Virtual Machine (JVM) can't find a required class definition at runtime. This can happen for a variety of reasons, including: