I want to install a specific JDK (the latest for example). For this, I went to the JDK download homepage: http://java.sun.com/javase/downloads/index.jsp. I looked for a Mac
The easiest way is to use Homebrew. Install Homebrew and then:
brew tap caskroom/versions
brew cask install java7
You can list all available versions using the following command:
brew cask search java
If you installed brew, cmd below will be helpful:
brew cask install java
As the message says, you have to go to Apple, not Sun, for Java on the Mac. As far as I know, Apple JDK 6 is installed by default on Mac OS X 10.6 (Snow Leopard). Maybe you need to install the developer tools from your Mac OS X installation DVD (the dev tools are an optional install from the OS DVD).
See: http://developer.apple.com/java/
NOTE This answer from 16 Oct 2009 is now outdated; you can get the JDK for Mac OS X from the regular JDK download page on Oracle's website now.
Mac comes with the JDK, for more information check:
http://developer.apple.com/mac/library/documentation/Java/Conceptual/Java14Development/02-JavaDevTools/JavaDevTools.html
JDK is the Java Development Kit (used to develop Java software).
JRE is the Java Runtime Environment (used to run any .jar file 'Java software').
The JDK contains a JRE inside it.
On Windows when you update Java, it updates the JRE automatically.
On Mac you do not have a JRE separated you have it, but inside the JDK, so when you update Java it will update your JRE which is inside your JDK; it doesn't install an JDK for you. You need to get it from somewhere else.
As of Mac OS X v10.6 (Snow Leopard), you can run Java 6 in 32-bit mode on either 32-bit or 64-bit Intel processor equipped Macs.
If you cannot upgrade to Snow Leopard, Soy Latte is a pre-compiled version of Java 6 for Intel 32-bit.