diff --git a/part_2/exercise_3/.gitignore b/part_2/exercise_3/.gitignore
new file mode 100644
index 0000000000000000000000000000000000000000..d578053fb6c37346e61ef9da56c648dac284bc98
--- /dev/null
+++ b/part_2/exercise_3/.gitignore
@@ -0,0 +1,30 @@
+### IntelliJ IDEA ###
+/.idea/
+out/
+!**/src/main/**/out/
+!**/src/test/**/out/
+
+### Eclipse ###
+.apt_generated
+.classpath
+.factorypath
+.project
+.settings
+.springBeans
+.sts4-cache
+bin/
+!**/src/main/**/bin/
+!**/src/test/**/bin/
+
+### NetBeans ###
+/nbproject/private/
+/nbbuild/
+/dist/
+/nbdist/
+/.nb-gradle/
+
+### VS Code ###
+.vscode/
+
+### Mac OS ###
+.DS_Store
\ No newline at end of file
diff --git a/part_2/exercise_3/exercise_3.iml b/part_2/exercise_3/exercise_3.iml
new file mode 100644
index 0000000000000000000000000000000000000000..c90834f2d607afe55e6104d8aa2cdfffb713f688
--- /dev/null
+++ b/part_2/exercise_3/exercise_3.iml
@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<module type="JAVA_MODULE" version="4">
+ <component name="NewModuleRootManager" inherit-compiler-output="true">
+ <exclude-output />
+ <content url="file://$MODULE_DIR$">
+ <sourceFolder url="file://$MODULE_DIR$/src" isTestSource="false" />
+ </content>
+ <orderEntry type="inheritedJdk" />
+ <orderEntry type="sourceFolder" forTests="false" />
+ </component>
+</module>
\ No newline at end of file
diff --git a/part_2/exercise_3/src/CommandLineApp.java b/part_2/exercise_3/src/CommandLineApp.java
new file mode 100644
index 0000000000000000000000000000000000000000..f1ec57b189cbd41fcce0db0b4658642fb10b6ebe
--- /dev/null
+++ b/part_2/exercise_3/src/CommandLineApp.java
@@ -0,0 +1,92 @@
+import java.util.Scanner;
+
+public class CommandLineApp {
+ private final LoanCalculator loanCalculator;
+
+ /*
+ * @.pre: loanCalculator != null
+ * @.post: object is constructed.
+ */
+ public CommandLineApp(LoanCalculator loanCalculator) {
+ this.loanCalculator = loanCalculator;
+ }
+
+ /*
+ * Ask for information from the user, then calculate and display monthly installment.
+ *
+ * @.pre: true
+ * @.post: print the monthly installment.
+ */
+ public void run() {
+ while (true) {
+ try {
+ Loan loan = createLoanFromUserInput();
+ double monthlyInstallment = loanCalculator.calculateMonthlyInstallment(loan);
+ displayMonthlyInstallment(monthlyInstallment);
+
+ break;
+ } catch (LoanCalculationException e) {
+ System.out.println("Error: " + e.getMessage());
+ }
+ }
+ }
+
+ private Loan createLoanFromUserInput() {
+ Loan loan;
+
+ Scanner reader = new Scanner(System.in);
+
+ while (true) {
+ try {
+ double principleAmount = getInputPrincipleAmount(reader);
+ int loanTermInMonths = getInputLoanTerm(reader);
+
+ loan = new Loan(principleAmount, loanTermInMonths);
+
+ break;
+ } catch (ZeroOrNegativePrincipleAmountException|DisallowedLoanTermException e) {
+ System.out.println("Error: " + e.getMessage());
+ }
+ }
+
+ return loan;
+ }
+
+ private void displayMonthlyInstallment(double installment) {
+ System.out.println("Monthly installment: " + installment);
+ }
+
+ private double getInputPrincipleAmount(Scanner reader) {
+ double principleAmount;
+
+ while (true) {
+ try {
+ System.out.print("Principle amount: ");
+ principleAmount = Double.parseDouble(reader.nextLine());
+
+ break;
+ } catch (NumberFormatException e) {
+ System.out.println("Error: Please enter a number");
+ }
+ }
+
+ return principleAmount;
+ }
+
+ private int getInputLoanTerm(Scanner reader) {
+ int loanTermInMonths;
+
+ while (true) {
+ try {
+ System.out.print("Loan term (in months): ");
+ loanTermInMonths = Integer.parseInt(reader.nextLine());
+
+ break;
+ } catch (NumberFormatException e) {
+ System.out.println("Error: Please enter an integer number");
+ }
+ }
+
+ return loanTermInMonths;
+ }
+}
diff --git a/part_2/exercise_3/src/Loan.java b/part_2/exercise_3/src/Loan.java
new file mode 100644
index 0000000000000000000000000000000000000000..f1d1eee8d5826c3055628a94a157eec8d56f5136
--- /dev/null
+++ b/part_2/exercise_3/src/Loan.java
@@ -0,0 +1,33 @@
+/*
+ * @.classInvariant:
+ * principleAmount() > 0 && 0 <= loanTermInMonths() <= 300
+ */
+public record Loan(double principleAmount, int loanTermInMonths) {
+ /*
+ * @.pre: true
+ * @.post: Object is constructed
+ * throw ZeroOrNegativePrincipleAmountException if principleAmount is less than or equal zero
+ * throw DisallowedLoanTermException if loanTermInMonths < 0 || loanTermInMonths > 300
+ */
+ public Loan {
+ if (principleAmount <= 0) {
+ throw new ZeroOrNegativePrincipleAmountException("Principle amount should be greater than zero");
+ }
+
+ if (loanTermInMonths < 0 || loanTermInMonths > 300) {
+ throw new DisallowedLoanTermException("Loan term in months allowed range 0-300");
+ }
+ }
+}
+
+class ZeroOrNegativePrincipleAmountException extends RuntimeException {
+ public ZeroOrNegativePrincipleAmountException(String message) {
+ super(message);
+ }
+}
+
+class DisallowedLoanTermException extends RuntimeException {
+ public DisallowedLoanTermException(String message) {
+ super(message);
+ }
+}
\ No newline at end of file
diff --git a/part_2/exercise_3/src/LoanCalculator.java b/part_2/exercise_3/src/LoanCalculator.java
new file mode 100644
index 0000000000000000000000000000000000000000..ed8ab95414a04c40e689d46ede95623aca5f6454
--- /dev/null
+++ b/part_2/exercise_3/src/LoanCalculator.java
@@ -0,0 +1,16 @@
+public interface LoanCalculator {
+ /*
+ * Calculate monthly installment based on principle amount and loan term (in months).
+ *
+ * @.pre: loan != null
+ * @.post: RESULT >= 0.
+ * throw LoanCalculationException if there is an error in calculation
+ */
+ double calculateMonthlyInstallment(Loan loan) throws LoanCalculationException;
+}
+
+class LoanCalculationException extends RuntimeException {
+ public LoanCalculationException(String message) {
+ super(message);
+ }
+}
\ No newline at end of file
diff --git a/part_2/exercise_3/src/Main.java b/part_2/exercise_3/src/Main.java
new file mode 100644
index 0000000000000000000000000000000000000000..33a7f1973e0d6243ff31855619caa8e78d873c04
--- /dev/null
+++ b/part_2/exercise_3/src/Main.java
@@ -0,0 +1,7 @@
+public class Main {
+ public static void main(String[] args) {
+ LoanCalculator calculator = new SimpleLoanCalculator();
+ CommandLineApp app = new CommandLineApp(calculator);
+ app.run();
+ }
+}
\ No newline at end of file
diff --git a/part_2/exercise_3/src/SimpleLoanCalculator.java b/part_2/exercise_3/src/SimpleLoanCalculator.java
new file mode 100644
index 0000000000000000000000000000000000000000..527c73c79b041af7b592f560060f4acb15052721
--- /dev/null
+++ b/part_2/exercise_3/src/SimpleLoanCalculator.java
@@ -0,0 +1,23 @@
+public class SimpleLoanCalculator implements LoanCalculator {
+ /*
+ * Calculate monthly installment with simple formula
+ *
+ * @.pre: loan != null
+ * @.post: RESULT >= 0.
+ * throw ZeroLoanTermException when loan term is equal to zero.
+ */
+ @Override
+ public double calculateMonthlyInstallment(Loan loan) throws LoanCalculationException {
+ if (0 == loan.loanTermInMonths()) {
+ throw new ZeroLoanTermException("Loan term should be greater than zero");
+ }
+
+ return loan.principleAmount() / loan.loanTermInMonths() + loan.principleAmount() / 240;
+ }
+}
+
+class ZeroLoanTermException extends LoanCalculationException {
+ public ZeroLoanTermException(String message) {
+ super(message);
+ }
+}
\ No newline at end of file