java notes

Objects
• A variable that can refer to an object does not
always have an object to refer to.
• In our program the variable str1 refers to an object
only after the new operator creates one.
• Before the new operator did its work, str1 was a
"place holder" that did not actually refer to any
object.
• After the new operator creates the object, str1 is
used to refer to the object.

Class
• A group of objects with similar properties and
behaviors is described by a class.
• Class is a pattern for an object.
• A class contains fields and methods that define
the behavior of the object.
• A class is a description of a kind of object.
• A programmer may define a class using Java, or
may use predefined classes that come in class
libraries such as the JDK.

Objected-oriented Programming