10.19
Random学习，发现一个很有趣的网站http://programmingbydoing.com/，主要是觉得程序后面的问题，很有利于刚开始学习的我有帮助，所以记录下来。
import java.util.Random; public class Randomness { public static void main ( String[] args ) { Random r = new Random(); int x = 1 + r.nextInt(10); System.out.println( "My random number is " + x ); System.out.println( "Here are some numbers from 1 to 5!" ); System.out.print( 1 + r.nextInt(5) + " " ); System.out.print( 1 + r.nextInt(5) + " " ); System.out.print( 1 + r.nextInt(5) + " " ); System.out.print( 1 + r.nextInt(5) + " " ); System.out.print( 1 + r.nextInt(5) + " " ); System.out.print( 1 + r.nextInt(5) + " " ); System.out.println(); System.out.println( "Here are some numbers from 1 to 100!" ); System.out.print( 1 + r.nextInt(100) + "\t" ); System.out.print( 1 + r.nextInt(100) + "\t" ); System.out.print( 1 + r.nextInt(100) + "\t" ); System.out.print( 1 + r.nextInt(100) + "\t" ); System.out.print( 1 + r.nextInt(100) + "\t" ); System.out.print( 1 + r.nextInt(100) + "\t" ); System.out.println(); int num1 = 1 + r.nextInt(10); int num2 = 1 + r.nextInt(10); if ( num1 == num2 ) { System.out.println( "The random numbers were the same! Weird." ); } if ( num1 != num2 ) { System.out.println( "The random numbers were different! Not too surprising, actually." ); } } }
后面的几个问题，觉得很有趣就都试了一下，
1.Delete the 1 + in front of all six lines that pick numbers 1-5, so that they look like this: System.out.print( r.nextInt(5) + " " ); Run the program a few times, and see if you can figure out what range the new random numbers are in.
结果试了几次，发现原来RANDOM是从0开始到N-1的
2.Change the 1 + in front of all six lines that pick numbers 1-5, so that they look like this: System.out.print( 3 + r.nextInt(5) + " " ); Run the program a few times. Is it picking random numbers from 3 to 5? If not, what range are they?
试了几次发现这种表达式只是在RANDOM 数种增加了一个确定的值。
3.Change the line where you create the random number generator so that it looks like this: Random r = new Random(12353); This number is called a seed. Run the program a few times. What do you notice? What happened to the random numbers?
我运行了几次之后发现，每次都结果都是一样的。查了API文件里面是这样写的：
使用SEED种子产生随机数，产生的数据会被保持。
方法是：
4.Change to random seed to something else and observe the behavior. What happens to the random numbers?
还是保持不变，但我把种子改成了3456，随机数据与种子是12345时不同了，应该是上面setSeed方法导致的。
最后是找到的在线文档，方便学习：http://tool.oschina.net/apidocs/apidoc?api=jdk_7u4
原文：http://www.cnblogs.com/missTS/p/4892807.html