Java02.md

Packages and Import

packages: all java classes grouped togather inside it (directory)

• should start with packge decleration:
  • package statment
  • imports
  • class

import Option

1. import javax.swing.*; // Make all classes visible altho only one is used.
2. import javax.swing.JOptionPane; // Make a single class visible.
3. Alternately we can the fully qualified class name without an import.

• javax.swing.JOptionPane.showMessageDialog(null, "Hi");

NOTES :

• import only tells the compiler where to look for symbols.
• The search for names is very efficient so there is no effective difference.
• The wildcard "*" only makes the classes in this package visible, not any of the subpackages.
• All classes in the java.lang package are visible without an import.

Different types of loops in Java

looping is a feature which facilitates the execution of a set of instructions until the controlling Boolean-expression evaluates to false.

• types of loops:

• Simple for loop : control structure that allows us to repeat certain operations by incrementing and evaluating a loop counter.

• While loop: repeats a statement or a block of statements while its controlling Boolean-expression is true.:

• Do-While loop: first condition evaluation happens after the first iteration of the loop.