OBJECTS AND CLASSES - Introduction to Java Programming: Comprehensive Version - page 335

You can use the no-arg constructor in the Date class to create an instance for the cur-
rent date and time, the getTime() method to return the elapsed time since January 1, 1970,
GMT, and the toString() method to return the date and time as a string. For example, the
following code

java.util.Date date = new java.util.Date();
System.out.println( "The elapsed time since Jan 1, 1970 is " +
date.getTime() + " milliseconds" );
System.out.println(date.toString());

create object

get elapsed time
invoke toString

displays the output like this:

The elapsed time since Jan 1, 1970 is 1324903419651 milliseconds
Mon Dec 26 07:43:39 EST 2011

The Date class has another constructor, Date(long elapseTime) , which can be used to
construct a Date object for a given time in milliseconds elapsed since January 1, 1970, GMT.

9.6.2 The Random Class
You have used Math.random() to obtain a random double value between 0.0 and 1.0
(excluding 1.0 ). Another way to generate random numbers is to use the java.util.Random
class, as shown in Figure 9.11, which can generate a random int , long , double , float , and
boolean value.

java.util.Random

+Random()
+Random(seed: long)
+nextInt(): int
+nextInt(n: int): int
+nextLong(): long
+nextDouble(): double
+nextFloat(): float
+nextBoolean(): boolean

Constructs a Random object with the current time as its seed.
Constructs a Random object with a specified seed.
Returns a random int value.
Returns a random int value between 0 and n (excluding n ).
Returns a random long value.
Returns a random double value between 0.0 and 1.0 (excluding 1.0 ).
Returns a random float value between 0.0F and 1.0F (excluding 1.0F ).
Returns a random boolean value.

F IGURE 9.11

A Random object can be used to generate random values.

When you create a Random object, you have to specify a seed or use the default seed. A
seed is a number used to initialize a random number generator. The no-arg constructor cre-
ates a Random object using the current elapsed time as its seed. If two Random objects have
the same seed, they will generate identical sequences of numbers. For example, the following
code creates two Random objects with the same seed, 3 .

Random random1 = new Random( 3 );
System.out.print( "From random1: " );
for ( int i = 0 ; i < 10 ; i++)
System.out.print(random1.nextInt( 1000 ) + " " );

Random random2 = new Random( 3 );
System.out.print( "\nFrom random2: " );
for ( int i = 0 ; i < 10 ; i++)
System.out.print(random2.nextInt( 1000 ) + " " );