The information we manage in a Java program is either primitive data or objects.
An abstraction hides details. A good abstraction hides the right details at the right time.
A variable is a name for a memory location used hold a value of a particular data type.
A variable can store only one value of its declared type.
Java is a strongly typed language. Each variable has a specific type, and we cannot assign a value of one type to a variable of another type.
Constants are like variables, but they hold one particular value.
Java has two kinds of numeric values: integers and floating point. The primitive type int is an integer data type and double is a floating point data type.
Many programming statements involve expressions. Expressions are combinations of one or more operands and the operators used to per form a calculation.
Java has rules that govern the order in which operators will be evaluated in an expression.
Avoid narrowing conversions because they can lose information.
The new operator returns a reference to a newly created object.
The Java standard class library is a useful set of classes that anyone can use when writing Java programs.