Java编程实例：计算阶乘的四个例子分享

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<p >这里有四个关于计算阶乘的，难度依次提升，全部通过测试。<p ><p >这应该是基本代码了，与之共勉。<p ><p >这是利用简单的循环相乘制造的阶乘。<p ><p ><p ><p >     public class Factorial { <p >public static int factorial(int x) { <p >if (x < 0) { <p >throw new IllegalArgumentException("x must be>=0"); <p >} <p >int fact = 1; <p >for (int i = 2; i <= x; i++) { <p >fact *= i; <p >} <p >return fact; <p >} <p >public static void main(String args[]) { <p >System.out.print(factorial(10)); <p >} <p >} <p ><p ><p >这个是利用递归算法制成的。<p ><p ><p ><p >　public class factorial2 { <p >public static int factorial2(int x) { <p >if (x < 0) { <p >throw new IllegalArgumentException("x must be>=0"); <p >} <p >if (x <= 1) { <p >return 1; <p >} else <p >return x * factorial2(x - 1); <p >} <p >public static void main(String args[]) { <p >System.out.print(factorial2(10)); <p >} <p >} <p ><p ><p >这个是数组添加的方法制成的，可以计算更大的阶乘。<p ><p ><p ><p >public class Factorial3 { <p >static long[] table = new long[21]; <p >static {table[0] = 1; } <p >static int last = 0; <p >public static long factorial(int x) throws IllegalArgumentException { <p >if (x >= table.length) { <p >throw new IllegalArgumentException("Overflow; x is too large."); <p >} <p >if (x <= 0) { <p >throw new IllegalArgumentException("x must be non-negative."); <p >} <p >while (last < x) { <p >table[last + 1] = table[last] * (last + 1); <p >last++; <p >} <p >return table[x]; <p >} <p >public static void main(String[] args) { <p >System.out.print(factorial(17)); <p >} <p >} <p ><p ><p >最后一个是利用BigInteger类制成的，这里可以用更大的更大的阶乘。<p ><p >    import java.math.BigInteger; <p >import java.util.*; <p >public class Factorial4{ <p >protected static ArrayList table = new ArrayList(); <p >static{ table.add(BigInteger.valueOf(1));} <p >public static synchronized BigInteger factorial(int x){ <p >for(int size=table.size();size<=x;size++){ <p >BigInteger lastfact= (BigInteger)table.get(size-1); <p >BigInteger nextfact= lastfact.multiply(BigInteger.valueOf(size)); <p >table.add(nextfact); <p >} <p >return (BigInteger) table.get(x); <p >} <p >public static void main(String[] args) { <p >System.out.print(factorial(17)); <p >} <p >} <p >< align=right></P><p align="center"></p></p>