What is the purpose of java.math.MutableBigInteger?

Question

java.math.MutableBigInteger is only available from inside the package. It inherits from java.lang.Object and there is only one subclass (Sign

Answer 1

MutableBigInteger is referenced in the java.math library. If you have a JDK installed check out the contents of src.zip in your jdk directory.

You will see BigInteger uses it:

public BigInteger divide(BigInteger val) {
    MutableBigInteger q = new MutableBigInteger(),
                      r = new MutableBigInteger(),
                      a = new MutableBigInteger(this.mag),
                      b = new MutableBigInteger(val.mag);

    a.divide(b, q, r);
    return new BigInteger(q, this.signum * val.signum);
}

MutableBigInteger is an encapsulation of the mathematical algorithms used by BigInteger.