JAVA 处理 大数 POJ1001
由于种种原因最近一段时间一直情绪不佳，写几个水题娱乐一下。
话说去年寒假学了点JAVA，写了些推箱子之类的东东，但还从来没有用JAVA A过题，很早就听说JAVA直接用大数类做大数和高精度手段很是淫荡，今天就来水几把寻点乐子。
POJ1001
Description
Problems involving the computation of exact values of very large magnitude and precision are common. For example, the computation of the national debt is a taxing experience for many computer systems.
This problem requires that you write a program to compute the exact value of R n where R is a real number ( 0.0 < R < 99.999 ) and n is an integer such that 0 < n <= 25.
This problem requires that you write a program to compute the exact value of R n where R is a real number ( 0.0 < R < 99.999 ) and n is an integer such that 0 < n <= 25.
Input
The input will consist of a set of pairs of values for R and n. The R value will occupy columns 1 through 6, and the n value will be in columns 8 and 9.
Output
The output will consist of one line for each line of input giving the exact value of R^n. Leading zeros should be suppressed in the output. Insignificant trailing zeros must not be printed. Don't print the decimal point if the result is an integer.
Sample Input
95.123 12 0.4321 20 5.1234 15 6.7592 9 98.999 10 1.0100 12
Sample Output
548815620517731830194541.899025343415715973535967221869852721 .00000005148554641076956121994511276767154838481760200726351203835429763013462401 43992025569.928573701266488041146654993318703707511666295476720493953024 29448126.764121021618164430206909037173276672 90429072743629540498.107596019456651774561044010001 1.126825030131969720661201
代码：
import java.util.*;
import java.math.*;
import java.io.*;
public class poj1001 {
public static void main(String args[])
{
Scanner cin = new Scanner(System.in);
while(cin.hasNext())
{
String a = cin.next();
int t = cin.nextInt();
BigDecimal ans = new BigDecimal(a);
ans = ans.pow(t);
String result = ans.stripTrailingZeros().toPlainString();
if(result.charAt(0)=='0') result=result.substring(1);
System.out.println(result);
}
}
}
add(),subtract(),pow(),abs()之类的常用运算方法都有，直接拿来用就行了。
BigDecimal关于格式控制的方法多了几个，这对处理各种不同格式的输出是很有用的。
stripTraillingZeros():把不影响数值大小的0全去掉；
1.50 ->1.5；
1.00->1;
这功能很有用吧。
大家都知道JAVA的类一般都要带toString这个方法的，BigDecimal则有toString,toPlainString和toEngineeringString三种表示成字符串的方法，
下面是这三种方法各自的特点：
toString: using scientific notation if an exponent is needed;
toEngineeringString:using engineering notation if an exponent is needed.
toPlainString:without an exponent field.