The security problems with Java are browser plugin issues. Any serious breech requires an unpatched hole in the plugin, plus an unpatched hole in the OS. In Windows, do all of non-admin stuff on a standard user login, keep your OS, browser, and Java up-to-date, and your vulnerablility will be very small. With or without Java, it's never zero.
Download system software only from official sources. For Java, that's either java.com, or oracle.com. Both are Oracle-sponsored sites, and Oracle is the owner of the Java trademark and technology. If you don't plan to write your own Java programs, java.com is easier to use.
http://www.java.com
If you do decide to dive into Java programming, the Oracle TechNetwork downloads are at:
http://www.oracle.com/technetwork/java/javase/downloads/index.html
You can also get the runtime (JRE) there. For Minecraft, make sure it's the Java 7 JRE (*not* "Server JRE") for your OS (including correct 32/64 bit choice). Minecraft doesn't officially support Java 8 yet.
https://help.mojang.com/customer/portal/articles/325948-minecraft-system-requirements