java zero - How do i compare values of BigInteger to be used as a condition in a loop?




operator type (4)

You can compare them using BigInteger.compareTo(BigInteger).

In your case, this would be while (base.compareTo(prime) > 0) {...}.

Also, your termination condition should be changed from if (a != one) to if (!a.equals(one)) since two BigInteger variables with the same integer value are not necessarily referencing the same object (which is all that == and != test).

I am trying to compare if the value of one BigInteger(base) is > the value of another BigInteger(prime) and if the value of 'a' is not equal to one. If value of a is not 1, it should break out of the loop. How should i compare them?

 Random ran = new Random();
    BigInteger prime = new BigInteger(16,ran);
    BigInteger base,a,one;
    one = new BigInteger("1");

    for (int i = 0; i < 65535; i++){

        while (base>prime){
            base = new BigInteger(16,ran);
        }
        a = base.modPow(prime.subtract(one),prime);
        System.out.println("a: "+a);    
        if (a != one){
            break;          
        }   
    }

Since BigIntegers are objects, you should use caution when using the equality operators. Right now, you're performing a reference comparison (which in this case, will more than likely fail). You'll need to use the equals() or compareTo() methods.

BigInteger has a built-in static variable representing one. Use the equals() method or the compareTo() method to compare values:

if (!a.equals(BigInteger.ONE)) {
    ...
}

-or-

if (a.compareTo(BigInteger.ONE) != 0) {
    ...
}

Hope that helps! See here for more information: http://download.oracle.com/javase/6/docs/api/java/math/BigInteger.html


Maybe

while (base.compareTo(prime)>0){
//rest of your loop
}

Apart from these above answers, I would like to add several functions:

    public static int parseIntOrDefault(String value, int defaultValue) {
    int result = defaultValue;
    try {
      result = Integer.parseInt(value);
    } catch (Exception e) {

    }
    return result;
  }

  public static int parseIntOrDefault(String value, int beginIndex, int defaultValue) {
    int result = defaultValue;
    try {
      String stringValue = value.substring(beginIndex);
      result = Integer.parseInt(stringValue);
    } catch (Exception e) {

    }
    return result;
  }

  public static int parseIntOrDefault(String value, int beginIndex, int endIndex, int defaultValue) {
    int result = defaultValue;
    try {
      String stringValue = value.substring(beginIndex, endIndex);
      result = Integer.parseInt(stringValue);
    } catch (Exception e) {

    }
    return result;
  }

And here are results while you running them:

  public static void main(String[] args) {
    System.out.println(parseIntOrDefault("123", 0)); // 123
    System.out.println(parseIntOrDefault("aaa", 0)); // 0
    System.out.println(parseIntOrDefault("aaa456", 3, 0)); // 456
    System.out.println(parseIntOrDefault("aaa789bbb", 3, 6, 0)); // 789
  }




java biginteger