Java求素数和最大公约数的简单代码示例

public class Primes {     public static void main(String[] args) {     // 求素数     List<Integer> primes = getPrimes(100000);       // 输出结果     for (int i = 0; i < primes.size(); i++) {       Integer prime = primes.get(i);       System.out.printf("%8d", prime);       if (i % 10 == 9) {         System.out.println();       }     }   }     /**    * 求 n 以内的所有素数    *    * @param n 范围    *    * @return n 以内的所有素数    */   private static List<Integer> getPrimes(int n) {     List<Integer> result = new ArrayList<Integer>();     result.add(2);      for (int i = 3; i <= n; i += 2) {       if (!divisible(i, result)) {         result.add(i);       }     }       return result;   }     /**    * 判断 n 是否能被整除    *    * @param n   要判断的数字    * @param primes 包含素数的列表    *    * @return 如果 n 能被 primes 中任何一个整除，则返回 true。    */   private static boolean divisible(int n, List<Integer> primes) {     for (Integer prime : primes) {       if (n % prime == 0) {         return true;       }     }     return false;   } } 

public class FractionTest {     public static void main(String[] args) {     Fraction a = new Fraction(7, 32);     Fraction b = new Fraction(13, 32);     System.out.println(a + " + " + b + " = " + a.add(b) + "(" + a.add(b).doubleValue() + ")");     System.out.println(a + " - " + b + " = " + a.minus(b) + "(" + a.minus(b).doubleValue() + ")");     System.out.println(a + " * " + b + " = " + a.multiply(b) + "(" + a.multiply(b).doubleValue() + ")");     System.out.println(a + " / " + b + " = " + a.devide(b) + "(" + a.devide(b).doubleValue() + ")");   } }   // 分数 class Fraction {   private int numerator;   // 分子     private int denominator;  // 分母     Fraction(int numerator, int denominator) {     if (denominator == 0) {       throw new IllegalArgumentException("分母不能为 0");     }       this.numerator = numerator;     this.denominator = denominator;     shrink();   }     Fraction() {     this(0, 1);   }     public int getNumerator() {     return numerator;   }     public void setNumerator(int numerator) {     this.numerator = numerator;   }     public int getDenominator() {     return denominator;   }     public void setDenominator(int denominator) {     this.denominator = denominator;   }     // 分子分母同除以最大公约数   private Fraction shrink() {     int maxCommonDivisor = getMaxCommonDivisor(this.denominator, this.numerator);     this.numerator /= maxCommonDivisor;     this.denominator /= maxCommonDivisor;     return this;   }     // 辗转相除法求最大公约数   private int getMaxCommonDivisor(int a, int b) {     int mod = a % b;       if (mod == 0) {       return b;     } else {       return getMaxCommonDivisor(b, mod);     }   }     // 分数加法   public Fraction add(Fraction that) {     return new Fraction(this.numerator * that.denominator + this.denominator * that.numerator,         this.denominator * that.denominator);   }     // 分数减法   public Fraction minus(Fraction that) {     return new Fraction(this.numerator * that.denominator - this.denominator * that.numerator,         this.denominator * that.denominator);   }     // 分数乘法   public Fraction multiply(Fraction that) {     return new Fraction(this.numerator * that.numerator,         this.denominator * that.denominator);   }     // 分数除法   public Fraction devide(Fraction that) {     return new Fraction(this.numerator * that.denominator,         this.denominator * that.numerator);   }     public double doubleValue() {     return (double) numerator / denominator;   }     @Override   public String toString() {     return String.format("{%d/%d}", this.numerator, this.denominator);   } } 

{7/32} + {13/32} = {5/8}(0.625){7/32} - {13/32} = {-3/16}(-0.1875){7/32} * {13/32} = {91/1024}(0.0888671875){7/32} / {13/32} = {7/13}(0.5384615384615384)