Java Basics

• A program consists of classes
• Classes might be packaged
• Classes have static parts and non-static parts
• Static parts always exist
• Non-static parts define what objects look like
• Objects are created with the new operator
• Classes have data and methods

• Files
• Comments
• import statments
• Class declarations
• Method declarations
• Statements

• One file
• One public class (same name as file)
• One main method
• Class methods and final class data as required

import <package hierarchy>.<class name> 

• General purpose classes in java.lang
  • All classes in java.lang are automatically imported by javac.
  • The Object class contains very general purpose things
  • The System class contains out with methods for printing on the screen.
    • System.out.print prints and leaves the cursor at the end of the output.
    • System.out.println prints and moves the cursor to the start of the next line.
    • PrintScanPrint.java
  • The String class contains string manipulation.
• The Scanner class in java.util contains methods for reading data from the keyboard
  • String next() - Reads the next word.
  • String nextLine() - Reads until the end of the line.
  • byte nextByte(), short nextShort(), int nextInt(), long nextLong() - Reads the next integer as a byte, short, int, or long.
  • float nextFloat(), double nextDouble() - Reads the next real number as a float or double.
  • boolean nextBoolean() - Reads the next boolean.