Which should I install — JDK or JRE — to run Java programs?

To run Java programs, you only need the JRE (Java Runtime Environment) because it contains the JVM (Java Virtual Machine) and the necessary libraries required to execute compiled Java code. However, if you want to write, compile, and run Java programs, you must install the JDK (Java Development Kit), as it includes both the compiler (javac) and the JRE. In short, JRE is for running Java applications, while JDK is for developing and running them.