StringMultiplication/src/de/janchristiangruenhage/math/multiplication/Multiplication.java

package de.janchristiangruenhage.math.multiplication;

import de.janchristiangruenhage.math.Number;
import de.janchristiangruenhage.math.addition.Addition;

/**
 * The class <tt>Multiplication</tt> represents a Multiplication fo two relatively large factors,
 * with about 25 digits per factor being a reasonable limit.
 */
public class Multiplication {
    private String factorOne;
    private String factorTwo;
    private int splitLines;
    private boolean highestMultiplication;
    private String carry;

    private String resultCarry;

    /**
     * Constructs a new Multiplication Object
     *
     * @param factorOne             First Factor
     * @param factorTwo             Second Factor
     * @param splitLines            How many lines of the multiplication will be added in one addition,
     *                              If != 0 and smaller than the number of digits in the second factor,
     *                              there will be multiple Additions per Multiplication.
     * @param highestMultiplication If this is a single or the top one of a row of multiplications,
     *                              there is no carry that will be passed over from this one to another Multiplication,
     *                              so the part that would be the carry has not to be enclosed in braces.
     */
    public Multiplication(String factorOne, String factorTwo, int splitLines, boolean highestMultiplication) {
        this.factorOne = factorOne;
        this.factorTwo = factorTwo;
        this.splitLines = splitLines;
        this.highestMultiplication = highestMultiplication;
        this.carry = "0";
        //Initializes carry as zero in case it is the lowest multiplication,
        //In case it is not set to another value later
    }

    /**
     * Creates and easily readable Multiplication and returns it.
     *
     * @return String representation of the Calculation
     */
    public String printCalculation() {
        String retVal = "";
        for (int i = 0; i < 2; i++) {
            retVal += "  ";
        }
        //Makes the First line some characters longer
        retVal += factorOne + " * " + factorTwo;
        //Adds the two factors and the Multiplication symbol to the first Line
        int lineLength = retVal.length();
        //Saves the length of the first line, this is needed later on since all lines need to have the same length
        retVal += "\n";
        for (int i = 0; i < lineLength; i++) {
            retVal += "_";
        }
        //Draws a line as the second line
        retVal += "\n";
        String[] lines;
        //array of lines, where the resulting addends will go to
        lines = new String[factorTwo.length() + 1];
        lines[lines.length - 1] = carry;
        //adds carry as last line
        while (lines[lines.length - 1].length() < (lineLength - 1)) {
            lines[lines.length - 1] = " " + lines[lines.length - 1];
            //elongates the carries line with spaces
        }
        lines[lines.length - 1] = "+" + lines[lines.length - 1];
        //adds a plus symbol to the carries line
        for (int i = 0; i < factorTwo.length(); i++) {
            //iterates through the second factor, therefore through the lines,
            // since there is a line for each digit  in the second factor
            lines[i] = "";
            //constructs the new line string
            int carry = 0;
            //creates new carry variable
            for (int j = 0; j < i; j++) {
                lines[i] = 0 + lines[i];
                //adds zeroes to the addends, depending on the digit they get multiplied with,
                //for example if its the line of the 3 in 344, then two zeroes get added
            }
            Number factorTwoNum = Number.parseNumber(factorTwo.charAt(factorTwo.length() - i - 1));
            //Parses the first one digit factor from the first factor string
            for (int j = 0; j < factorOne.length(); j++) {
                Number factorOneNum = Number.parseNumber(factorOne.charAt(factorOne.length() - j - 1));
                //Parses the second one digit factor from the first factor string
                Number result = Number.multiply(factorOneNum, factorTwoNum, carry);
                //Multiplies the factors, adds the carry after that
                carry = result.getCarry();
                //assigns the carry it's new value
                lines[i] = result.toString() + lines[i];
                //adds the result to the line
            }
            if (carry != 0) {
                lines[i] = carry + lines[i];
                //if there is a carry left in the end, it gets added to the same line
            }
            while (lines[i].length() < (lineLength - 1)) {
                lines[i] = " " + lines[i];
                //elongates the line with spaces
            }
            if (i > 0) {
                lines[i] = "+" + lines[i];
                //adds a plus symbol to the line
            } else {
                lines[i] = " " + lines[i];
                //adds another space to the line
            }
        }
        Addition addition = new Addition(lines, splitLines, factorOne.length(), !highestMultiplication);
        //Construct the new addition
        retVal += addition.printCalculation();
        //prints the addition and adds that to the retVal string
        resultCarry = addition.getResultCarry();
        //saves the resultCarry of the addition,
        // this is used for the higher multiplications, if there are any
        return retVal;
    }

    /**
     * Setter for the carry
     *
     * @param carry the carry
     */
    public void setCarry(String carry) {
        this.carry = carry;
    }

    /**
     * Getter for the carry of the result
     *
     * @return the carry of the result
     */
    public String getResultCarry() {
        return resultCarry;
    }
}