Some Standard Classes Chapter 13 1 For Next Time Read Chapter 13 - PowerPoint PPT Presentation

Some Standard Classes Chapter 13 1

For Next Time  Read Chapter 13 2

Packages  Classes can be organized into packages  The core classes reside in the java.lang package  No import is needed  Classes include System , String , Math , and the primitive type wrapper classes  java.util is another useful package 3

System class  The public out constant object provides the printing methods print() , println() , and printf()  currentTimeMillis() returns the system time as milliseconds since midnight, January 1, 1970  The exit() method terminates a running Java program 4

String class 5

Wrapper classes 6

Useful wrapper methods 7

DecimalFormat class  An alternative to System.out.printf()  Allows numbers to be formatted as strings  Define a format template string  # a number placeholder; number appears if necesssary  0 a number placeholder; zero always appears  Create a DecimalFormat object from the format template string  Use the format() method to create a string 8

Math class 9

A Math -worthy problem 10

Random class  Use to create pseudorandom number generator objects  Good enough for most purposes  Useful in games, simulations, and testing  nextInt() method returns a pseudorandom integer  If r is a Random object,  r.nextInt( n ) returns a psuedorandom integer from the range 0 … n – 1 11

Next . . . The object class . . . 12