test: adding subject and main

subjects/java/checkpoints/perfect-number/ExerciseRunner.java

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+public class ExerciseRunner {
+    public static void main(String[] args) {
+        PerfectNumber perfectNumber = new PerfectNumber();
+
+        // Test case 1
+        int number1 = 6;
+        System.out.println("Is " + number1 + " a perfect number? " + perfectNumber.isPerfectNumber(number1));
+
+        // Test case 2
+        int number2 = 28;
+        System.out.println("Is " + number2 + " a perfect number? " + perfectNumber.isPerfectNumber(number2));
+
+        // Test case 3
+        int number3 = 12;
+        System.out.println("Is " + number3 + " a perfect number? " + perfectNumber.isPerfectNumber(number3));
+    }
+}

subjects/java/checkpoints/perfect-number/README.md

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+## Perfect Number
+
+### Instructions
+
+Write a program to check if a given number is a perfect number. A perfect number is a positive integer that is equal to the sum of its proper positive divisors, excluding itself.
+
+### Expected Class
+
+```java
+public class PerfectNumber {
+    public boolean isPerfectNumber(int number) {
+        // Implementation to check if the given number is a perfect number
+    }
+}
+```
+
+### Usage
+
+Here is a possible `ExerciseRunner.java` to test your class:
+
+```java
+public class ExerciseRunner {
+    public static void main(String[] args) {
+        PerfectNumber perfectNumber = new PerfectNumber();
+
+        // Test case 1
+        int number1 = 6;
+        System.out.println("Is " + number1 + " a perfect number? " + perfectNumber.isPerfectNumber(number1));
+
+        // Test case 2
+        int number2 = 28;
+        System.out.println("Is " + number2 + " a perfect number? " + perfectNumber.isPerfectNumber(number2));
+
+        // Test case 3
+        int number3 = 12;
+        System.out.println("Is " + number3 + " a perfect number? " + perfectNumber.isPerfectNumber(number3));
+    }
+}
+```
+
+### Expected Output
+
+```shell
+$ javac *.java -d build
+$ java -cp build ExerciseRunner
+Is 6 a perfect number? true
+Is 28 a perfect number? true
+Is 12 a perfect number? false
+$
+```