Sun / Oracle releases of Java SE come in two forms: JRE and JDK. In simple terms, JREs support running Java applications, and JDKs also support Java development.
Java Runtime Environment or JRE distributions consist of the set of libraries and tools needed to run and manage Java applications. The tools in a typical modern JRE include:
javacommand for running a Java program in a JVM (Java Virtual Machine)
keytoolcommand for manipulating Java keystores.
policytoolcommand for editing security sandbox security policies.
unpack200tools for packing and unpacking "pack200" file for web deployment.
tnameservcommands that support Java CORBA and RMI applications.
"Desktop JRE" installers include a Java plugin suitable for some web browser. This is deliberately left out of "Server JRE" installers.linux syscall read benchmarku
From Java 7 update 6 onwards, JRE installers have included JavaFX (version 2.2 or later).
A Java Development Kit or JDK distribution includes the JRE tools, and additional tools for developing Java software. The additional tools typically include:
javaccommand, which compiles Java source code (".java") to bytecode files (".class").
appletviewerfor running applets
idljthe CORBA IDL to Java compiler
javahthe JNI stub generator
native2asciifor character set conversion of Java source code
schemagenthe Java to XML schema generator (part of JAXB)
serialvergenerate Java Object Serialization version string.
wsimportsupport tools for JAX-WS
jdbthe basic Java debugger
jhatfor dumping and analysing a Java heap.
jstackfor getting a thread stack dump.
javapfor examining ".class" files.
jconsolea management console,
jpsfor application monitoring
A typical Sun / Oracle JDK installation also includes a ZIP file with the source code of the Java libraries. Prior to Java 6, this was the only publicly available Java source code.
From Java 6 onwards, the complete source code for OpenJDK is available for download from the OpenJDK site. It is typically not included in (Linux) JDK packages, but is available as a separate package.