Chapter 2: Objects and Primitives

Objects and Primitive Data

  1. The information we manage in a Java program is either primitive data or objects.
  2. An abstraction hides details. A good abstraction hides the right details at the right time.
  3. A variable is a name for a memory location used hold a value of a particular data type.
  4. A variable can store only one value of its declared type.
  5. 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.
  6. Constants are like variables, but they hold one particular value.
  7. 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.
  8. Many programming statements involve expressions. Expressions are combinations of one or more operands and the operators used to per­ form a calculation.
  9. Java has rules that govern the order in which operators will be evaluated in an expression.
  10. Avoid narrowing conversions because they can lose information.
  11. The new operator returns a reference to a newly created object.
  12. The Java standard class library is a useful set of classes that anyone can use when writing Java programs.