Como instalar o Java

When installing Java you can install:

➔ JRE

➢ Java Runtime Environment
➢ Install if all you’re gonna do is run Java applications
➢ The JRE consists of the Java Virtual Machine (JVM): Java platform core classes, and supporting Java platform libraries on top of which Java applications will run.

➔ JDK

➢ Java Development Kit
➢ Also includes the JRE
➢ Install if you’re developing java in your PC, it’s got all tools for development namely compiling projects
➢ Needed when working with Eclipse / Ant / Maven / NetBeans ...

➔ If you’re working with e-lab on your computer then make sure you install the JDK

➢ Preferably use Java 6_45 but presently any version will work.

➔ Oracle’s JDK is recommended but you may also choose another JDK, like:

➢ Open JDK (for which you also need IcedTea WebStart plugin)
➢ For more info check these out: Simpler & +Complete

Installation for Windows

Just download Java; if you wish you can install a previous version from Java SE Runtime Environment 6u45 and install it according to Oracle instructions.

Installation for Linux

➔ Download the binnary: *.bin ➔ Go to the java installation directory

➢ Something like “/usr/lib/jvm/oracle-jdk”
➢ This must coincide with JAVA_HOME variable value for the path 

➔ Commands to install (example):

$ chmod a+x jre-6u30-linux-x64.bin
(Now we got it to be executable! lets install it!)
$ ./jre-6u30-linux-x64.bin
export JAVA_HOME="/usr/lib/jvm/oracle-jdk"
export PATH="$PATH:$JAVA_HOME/jre/bin:$JAVA_HOME/bin

More info here