Java: Unicode  
Unicode is a system of encoding characters. All characters and Strings in Java use the Unicode encoding, which allows truly international programming..

Variables and Types  
Data in memory is referred to by name. This is called a variable. You can think of a variable name as the human-usable equivalent of a memory address..

Numbers  
There are basically two kinds of numbers in Java and most other programming languages: binary integers (most commonly using the type int) and binary floating-point numbers (most commonly using the type double)..

Autoboxing  
Autoboxing, introduced in Java 5, is the automatic conversion the Java compiler makes between the primitive (basic) types and their corresponding object wrapper classes.

Boolean  
The primitive type boolean has only two possible values: true and false..

Floating-point  
Floating-point numbers are like real numbers in mathematics, for example, 3.14159, -0.000001..

Integers  
Java automatically converts decimal numbers you write in your source program into binary numbers internally..