我无法弄清楚我的简单Java作业

Error: Too many input characters error.

我在这方面工作了很长时间,但无法搞清楚.有人可以告诉我如何使重量转换像长度转换一样工作吗？

import java.util.Scanner;

/**
 * This class..
 */
public class UnitConversion3b
{
    public static void main(String[] args)   
    {
        Scanner keyboard = new Scanner(System.in);

        String maxInputWarning = "nError: Too many input characters."
        + "nProgram is now terminating.";
        String lengthOrWeight;
        final double LENGTH_CONVERSION_FACTOR = 3.2808399;
        final double WEIGHT_CONVERSION_FACTOR = 2.20462;
        String whichWeightConversion = "empty",whichLengthConversion = "empty";
        double feet = 0,meters = 0,pounds =0,kilograms = 0;
        double metersConvertedToFeet,feetConvertedToMeters;
        double poundsConvertedToKilograms,kilogramsConvertedToPounds;

        System.out.println("");
        System.out.print("What kind of value would you like to convert?");
        System.out.print("nEnter L for length,or W for weight: ");
        lengthOrWeight = keyboard.nextLine();
        if (lengthOrWeight.length() > 1 ) {
            System.out.println(maxInputWarning);
            System.out.print("Press Enter to continue ... ");
            keyboard.nextLine();
            return;
        } else if ((!(lengthOrWeight.equalsIgnoreCase("l"))
            && (!(lengthOrWeight.equalsIgnoreCase("w"))))){
            System.out.println("nError: Unrecognized conversion type."
            + "nProgram is now terminating.");
            System.out.print("Press Enter to continue ... ");
            keyboard.nextLine();
            return;
        } else if (lengthOrWeight.equalsIgnoreCase("l")){
            System.out.println("nConverting feet or meters?");
            System.out.print("Enter F to convert feet,or M for meters: "); 
            whichLengthConversion = keyboard.nextLine();
        }

        if (whichLengthConversion.length() > 1 ) {
            System.out.println(maxInputWarning);
            System.out.print("Press Enter to continue ... ");
            keyboard.nextLine();
            return;
        } else if ((!(whichLengthConversion.equalsIgnoreCase("f"))
            && (!(whichLengthConversion.equalsIgnoreCase("m"))))){
            System.out.println("nError: Unrecognized unit of "
            + "measurement.nProgram is now terminating."     );
            System.out.print("Press Enter to continue ... ");
            keyboard.nextLine();
            return;
        } else if (whichLengthConversion.equalsIgnoreCase("f")){
            System.out.print ("Enter the number of feet to"
            + " convert to meters: ");
            feet = keyboard.nextDouble();
            feetConvertedToMeters = feet / LENGTH_CONVERSION_FACTOR;
            System.out.println("The number of meters in " + feet +
            " feet is " + feetConvertedToMeters + ".");
            keyboard.nextLine();
            System.out.print("Press Enter to continue ... ");
            keyboard.nextLine();
            return;
        } else if (whichLengthConversion.equalsIgnoreCase("m")){
            System.out.print ("Enter the number of meters to"
            + " convert to feet: ");
            meters = keyboard.nextDouble();
            metersConvertedToFeet = meters * LENGTH_CONVERSION_FACTOR;
            System.out.println("The number of feet in " + meters +
            " meters is " + metersConvertedToFeet + ".");
            keyboard.nextLine();
            System.out.print("Press Enter to continue ... ");
            keyboard.nextLine();
            return;
        }

        if (lengthOrWeight.equalsIgnoreCase("w")){
            System.out.println("Converting pounds or kilograms?");
            System.out.print("Enter P to convert pounds,or K for kilograms: ");
            whichWeightConversion = keyboard.nextLine();
        }

        if (whichWeightConversion.length() > 1 ) { 
            System.out.println(maxInputWarning);
            System.out.print("Press Enter to continue ... ");
            keyboard.nextLine();
            return;
        } else if ((!(whichWeightConversion.equalsIgnoreCase("p"))
            && (!(whichWeightConversion.equalsIgnoreCase("k"))))){
            System.out.println("nError: Unrecognized unit of "
            + "measurement.nProgram is now terminating."     );
            System.out.print("Press Enter to continue ... ");
            return;
        } else if (whichWeightConversion.equalsIgnoreCase("p")){
            System.out.println("Enter the number of pounds to"
            + " convert to kilograms:");
            pounds = keyboard.nextDouble();
            poundsConvertedToKilograms = pounds / WEIGHT_CONVERSION_FACTOR;
            System.out.println("The number of pounds in " + kilograms +
            " kilograms is " + poundsConvertedToKilograms + ".");
            keyboard.nextLine();
            System.out.print("Press Enter to continue ... ");
            keyboard.nextLine();
            return;
        } else if (whichLengthConversion.equalsIgnoreCase("k")){
            System.out.print ("Enter the number of kilograms to"
            + " convert to pounds: ");
            kilograms = keyboard.nextDouble();
            kilogramsConvertedToPounds = kilograms * WEIGHT_CONVERSION_FACTOR;
            System.out.println("The number of pounds in " + pounds +
            "pounds is " + kilogramsConvertedToPounds + ".");
            keyboard.nextLine();
            System.out.print("Press Enter to continue ... ");
            keyboard.nextLine();
            return;

        } else{ 
            return;
        }
    }
}