Moose!
When this happens it could be a number of things, either you could have a problem with the demo itself where you may not have activated your account or it has run out or it could be a java error. To fix the java error I recommend simply installing the latest version.
Yes, you will need Java. I recommend installing the latest version of Java, JRE7, which I have provided a download link to it on Oracle's site just on the development of JRE7, it will highly increase Minecraft's performance. Also, Minecraft is coded in the Java language. It must be read with a Java program, and in your task manager, Minecraft is "javaw.exe" so a big yes!
Yes, Minecraft is a java-based game.
Minecraft was created in Java and uses Java to run, therefore you MUST have Java to play Minecraft.
Yes, Java is the platform Minecraft runs on. Java is free for download.
Recent changes to Minecraft have made it independent of Java.
Because Minecraft is built around Java, it is currently impossible to play Minecraft without Java.
The Minecraft Demo, on Java Edition is a version that has 100 minutes play-time and has the same seed every time you load it up, and stays the same on every platform it runs on. If you mean the Minecraft Pocket Edition Demo, or Lite, is an older version on v0.2.1 alpha2. The game has 18 available blocks and 36 were shown but unobtainable. The game is not on Google Play publicly for download, but users that downloaded the app beforehand can still have access to it in their app library.
If you want to play Minecraft in your web browser, you will have to install Java on your computer. Java usually comes with browser plugins that can be used to run Java apps such as Minecraft in your browser. You can download Java from Java's website.
You absolutely MUST have Java to play or run Minecraft, and there is no legal online version of Minecraft. You must download Minecraft to your computer.
Minecraft was coded using JAVA.
Yes, Minecraft works perfectly. Minecraft is programmed and runs on java, so that it can be played on a variety of platforms - including Mac, Windows, and Linux. If Minecraft doesn't work for you, you may have to update your version of Java.