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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 - - 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 ,
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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
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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
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String class
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Wrapper classes
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Useful wrapper methods
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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
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Math class
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A Math-worthy problem
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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
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