How-to articles, tricks, and solutions about JAVA

If GSON is throwing a JsonSyntaxException with the message "Expected BEGIN_OBJECT but was BEGIN_ARRAY", it means that you are trying to parse a JSON array as if it were a JSON object.

To get the first key-value pair from a HashMap in Java, you can use the entrySet() method to get a set of the map's entries and then use the iterator() method to get an iterator for the set.

To store multiple values under the same key in a HashMap in Java, you can use a List or an array as the value for the key.

To show the real SQL generated by Hibernate, you can enable the show_sql property in the Hibernate configuration file (hibernate.cfg.xml).

If you are using Hibernate and you see the error "MultipleBagFetchException: cannot simultaneously fetch multiple bags", it means that you are trying to fetch multiple collections of an entity using a single Hibernate query.

To make the Selenium WebDriver wait for a specified number of seconds in Java, you can use the Thread.sleep method. Here's an example of how you can do this:

To check if a single character appears in a string in Java, you can use the indexOf method of the String class.

To check if a value is of type Integer in Java, you can use the instanceof operator.

To check if an element exists with Selenium WebDriver, you can use the findElements() method of the WebDriver interface and check the size of the returned list.

To check if an array is null in Java, you can use the == operator and compare the array to null. For example:

To clear or empty a StringBuilder in Java, you can use the setLength method and set the length to 0.

To concatenate two arrays in Java, you can use the System.arraycopy method. Here's an example of how you can do this:

To convert a long value to an int value in Java, you can use the intValue method of the java.lang.Long class. This method returns the value of the specified long as an int.

To convert a stack trace to a string in Java, you can use the printStackTrace() method of the Throwable class, which prints the stack trace to a PrintWriter.

You can use the toArray() method of the List interface to convert a List<Integer> to an int[] in Java.

There are several ways to convert a Java program to an executable file (.exe):

It is generally not a good idea to intentionally create a memory leak in 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 download and save a file from the Internet using Java, you can use the URL and URLConnection classes from the java.net package.

A .jar file is a Java Archive file that contains compiled Java code and resources (such as images, sounds, etc.) that can be used by Java applications.

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 generate an MD5 hash in Java, you can use the MessageDigest class from the java.security package.

To generate a random number in a specific range in Android, you can use the nextInt method of the java.util.Random class.

To get the current date and time in UTC or GMT in Java, you can use the Instant class from the java.time package. The Instant class represents a single point in time in the ISO-8601 calendar system, with a resolution of nanoseconds.

To get the current stack trace in Java, you can use the getStackTrace method of the Thread class or the getStackTrace method of the Throwable class.