BAEL-3966: find object's class in Java (#9118)

core-java-modules/core-java/src/main/java/com/baeldung/objectclass/Borrower.java

@@ -0,0 +1,23 @@
+package com.baeldung.objectclass;
+
+import lombok.Data;
+
+@Data
+public class Borrower extends User {
+    
+    private double totalLoanAmount;
+    
+    public double requestLoan(double amount) {
+        totalLoanAmount = amount;
+        return totalLoanAmount;
+    }
+    
+    public double increaseLoan(double increaseBy) {
+        return totalLoanAmount + increaseBy;
+    }
+    
+    public double payLoan(double amount) {
+        return totalLoanAmount - amount;
+    }
+
+}

core-java-modules/core-java/src/main/java/com/baeldung/objectclass/Lender.java

@@ -0,0 +1,20 @@
+package com.baeldung.objectclass;
+
+public class Lender extends User {
+    
+    private double totalInvestmentAmount;
+    
+    public double invest(double amount) {
+        totalInvestmentAmount = amount;
+        return totalInvestmentAmount;
+    }
+    
+    public double increaseInvestment(double increaseBy) {
+        return totalInvestmentAmount + increaseBy;
+    }
+    
+    public double collectDividends() {
+        return totalInvestmentAmount * 0.07;
+    }
+
+}

core-java-modules/core-java/src/main/java/com/baeldung/objectclass/User.java

@@ -0,0 +1,12 @@
+package com.baeldung.objectclass;
+
+import lombok.Data;
+
+@Data
+public class User {
+    
+    private String firstName;
+    private String lastName;
+    
+
+}

core-java-modules/core-java/src/test/java/com/baeldung/objectclass/CreditAppUnitTest.java

@@ -0,0 +1,74 @@
+package com.baeldung.objectclass;
+
+import static org.junit.Assert.assertNotEquals;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertTrue;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.Test;
+
+public class CreditAppUnitTest {
+    
+    @Test
+    public void givenLender_whenInstanceOf_thenReturnTrue() {
+        User lender = new Lender();
+        assertTrue(lender instanceof Lender);
+        assertTrue(lender instanceof User);
+    }
+    
+    @Test
+    public void givenUser_whenInstanceOfLender_thenDowncast() {
+        User user = new Lender();
+        Lender lender = null;
+        
+        if(user instanceof Lender) {
+            lender = (Lender) user;
+        }
+        
+        assertNotNull(lender);
+    }
+    
+    @Test
+    public void givenUser_whenIsInstanceOfLender_thenDowncast() {
+        User user = new Lender();
+        Lender lender = null;
+        
+        if(Lender.class.isInstance(user)) {
+            lender = (Lender) user;
+        }
+        
+        assertNotNull(lender);
+    }
+    
+    @Test
+    public void givenBorrower_whenLoanAmountIsDouble_thenRequestLoan() {
+        Borrower borrower = new Borrower();
+        double amount = 100.0;
+        
+        //if(amount instanceof Double) // Compilation error, no autoboxing
+        if(Double.class.isInstance(amount)) {
+            borrower.requestLoan(amount);
+        }
+        assertEquals(100, borrower.getTotalLoanAmount());
+    }
+    
+    @Test
+    public void givenBorrower_whenLoanAmountIsNotString_thenRequestLoan() {
+        Borrower borrower = new Borrower();
+        Double amount = 100.0;
+        
+        //if(amount instanceof String) // Compilation error, incompatible operands
+        if(!String.class.isInstance(amount)) {
+            borrower.requestLoan(amount);
+        }
+        assertEquals(100, borrower.getTotalLoanAmount());
+    }
+    
+    @Test
+    public void givenLender_whenGetClass_thenEqualsLenderType() {
+        User lender = new Lender();
+        assertEquals(Lender.class, lender.getClass());
+        assertNotEquals(User.class, lender.getClass());
+    }
+
+}