A Java IDE that starts with the JDK already set up
The first hour of learning Java is often spent not writing Java. You download a JDK, find out where it installed, set JAVA_HOME, edit PATH, then install a full Java IDE that asks you to create a project, pick a build system and choose a package name before you can print a line. Java IDE removes all of that. The Microsoft Build of OpenJDK 25 comes bundled with the app, so it can compile and run Java on a PC that has never had Java on it.
Open or create a .java file and press F5. The source is compiled and launched using Java's single-file launcher, the same way java Main.java works from a terminal, and what the program prints streams into the output panel below the editor. There is no project to set up first: one file, one class with a main method, one key.
It is built for Java, the language of classes, objects and public static void main, not JavaScript, which only shares the name. Its limits are deliberate: there is no debugger and no Maven or Gradle, so it suits learning, exercises and single-file programs rather than a multi-module codebase.
How to run a Java program on Windows in three steps
The new-file starter is a small program that asks for your name with Scanner and greets you, so you can watch the whole loop work before you change anything.
- Press Ctrl+N for a new file, or Ctrl+O to open a .java file you already have.
- Press F5. The status bar shows which Java the run used.
- When the program waits for input, type into the box under the output and press Enter. Shift+F5 stops it.
Java compiler errors and exceptions in plain English
Javac is strict, and its wording assumes you already know the vocabulary. Each error appears in the Problems list as a line you can click to jump to the spot, and the most common ones get a one-sentence explanation alongside the original message.
That covers cannot find symbol (usually a spelling or capitalization slip, or a missing import), a missing semicolon, braces that do not pair up, incompatible types, a possible lossy conversion between number types, a missing return statement, a variable read before it was given a value, and the classic beginner trap of calling a non-static method from main.
Runtime exceptions are treated the same way and linked to the line in your file where they happened. NullPointerException, ArrayIndexOutOfBoundsException, StringIndexOutOfBoundsException, ArithmeticException from dividing by zero, NumberFormatException, and the Scanner pair InputMismatchException and NoSuchElementException each come with a short note on what went wrong.
A Java code runner for practice problems
Exercise sites and programming contests give you sample input to test against. Save it as input.txt in the same folder as your .java file and press Ctrl+F5: the file is fed to System.in and then closed, so a loop that reads while hasNext() is true ends cleanly. Leave Clear the output each run switched off in Settings to keep a history of runs in the panel and compare them.
Fifteen starter programs open in their own tabs, grouped as Basics, Objects, Collections, and Files and more. They range from reading a number and looping, through a class, a record and inheritance, to streams, counting words in a map, writing and reading a file, and a guess-the-number game.
