Separating calculations into methods simplifies modifying and expanding programs

Question

Separating calculations into methods simplifies modifying and expanding programs.

The following program calculates the tax rate and tax to pay, using methods. One method returns a tax rate based on an annual salary.

Run the program below with annual salaries of 40000, 60000, and 0.

Change the program to use a method to input the annual salary.

Run the program again with the same annual salaries as above. Are results the same?

This is the code including what I am working on added. I will not run. I need to remove some areas to designate the scanner as the source of input but I am unsure of which area.

import java.util.Scanner;

public class IncomeTax {
// Method to get a value from one table based on a range in the other table
public static double getCorrespondingTableValue(int search, int [] baseTable, double [] valueTable) {
int baseTableLength = baseTable.length;
double value = 0.0;
int i = 0;
boolean keepLooking = true;

i = 0;
while ((i < baseTableLength) && keepLooking) {
if (search <= baseTable[i]) {
value = valueTable[i];
keepLooking = false;
}
else {
++i;
}
}

return value;
}

public static void readInput(int salaryOne, int salaryTwo, int salaryThree);

annualSalary = 0;

Scanner scnr = new Scanner(System.in);
scnr nextInt();
new annualSalary;

public static void main (String [] args) {
Scanner scnr = new Scanner(System.in);
int annualSalary = 0;
double taxRate = 0.0;
int taxToPay = 0;
int i = 0;

int [] salaryBase = { 20000, 50000, 100000, 999999999 };
double [] taxBase = { .10, .20, .30, .40 };
  
// FIXME: Change the input to come from a method
System.out.println(" Enter annual salary (0 to exit): ");
annualSalary = scnr.nextInt();

while (annualSalary > 0) {
taxRate = getCorrespondingTableValue(annualSalary, salaryBase, taxBase);

taxToPay= (int)(annualSalary * taxRate); // Truncate tax to an integer amount
System.out.println("Annual salary: " + annualSalary +
" Tax rate: " + taxRate +
" Tax to pay: " + taxToPay);

// Get the next annual salary
// FIXME: Change the input to come from a method
System.out.println(" Enter annual salary (0 to exit): ");
annualSalary = scnr.nextInt();
}

return;
}
}

Explanation / Answer

IncomeTax.java

import java.util.Scanner;

public class IncomeTax {
   // Method to get a value from one table based on a range in the other table
   public static double getCorrespondingTableValue(int search, int [] baseTable, double [] valueTable) {
   int baseTableLength = baseTable.length;
   double value = 0.0;
   int i = 0;
   boolean keepLooking = true;
   i = 0;
   while ((i < baseTableLength) && keepLooking) {
   if (search <= baseTable[i]) {
   value = valueTable[i];
   keepLooking = false;
   }
   else {
   ++i;
   }
   }
   return value;
   }
   public static int readInput(Scanner scan){
       System.out.println(" Enter annual salary (0 to exit): ");
       int annualSalary = scan.nextInt();
       return annualSalary;
   }
   public static void main (String [] args) {
   Scanner scnr = new Scanner(System.in);
   int annualSalary = 0;
   double taxRate = 0.0;
   int taxToPay = 0;
   int [] salaryBase = { 20000, 50000, 100000, 999999999 };
   double [] taxBase = { .10, .20, .30, .40 };
  
   // FIXME: Change the input to come from a method
   annualSalary = readInput(scnr);
   while (annualSalary > 0) {
   taxRate = getCorrespondingTableValue(annualSalary, salaryBase, taxBase);
   taxToPay= (int)(annualSalary * taxRate); // Truncate tax to an integer amount
   System.out.println("Annual salary: " + annualSalary +
   " Tax rate: " + taxRate +
   " Tax to pay: " + taxToPay);
   // Get the next annual salary
   // FIXME: Change the input to come from a method
   annualSalary = readInput(scnr);
   }
   return;
   }
   }
     
Output:

Enter annual salary (0 to exit):
10000
Annual salary: 10000   Tax rate: 0.1   Tax to pay: 1000

Enter annual salary (0 to exit):
50000
Annual salary: 50000   Tax rate: 0.2   Tax to pay: 10000

Enter annual salary (0 to exit):
0

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