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)