Feature/grade

Calculator.java

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+public class Calculator {
+    // ADDITION
+    public double add(double a, double b) { return a + b; }
+    // SUBTRACTION
+    public double sub(double a, double b) { return a - b; }
+    // MULTIPLICATION
+    public double mul(double a, double b) { return a * b; }
+    // DIVISION
+    public double div(double a, double b) { 
+        if (b == 0) {
+            System.out.println("Error: Division by zero!");
+            return 0;
+        }
+        return a / b;
+     }
+}

Grade.java

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+public class Grade {
+    public String getLetterGrade(int score) {
+        if (score < 0 || score > 100) {
+            return "Invalid score";
+        } else if (score >= 80) {
+            return "A";
+        } else if (score >= 70) {
+            return "B";
+        } else if (score >= 50) {
+            return "C";
+        } else if (score >= 30) {
+            return "D";
+        } else {
+            return "F";
+        }
+    }
+
+    public double getGradePoint(int score) {
+        if (score < 0 || score > 100) {
+            return -1;
+        } else if (score >= 80) {
+            return 4.0;
+        } else if (score >= 70) {
+            return 3.0;
+        } else if (score >= 50) {
+            return 2.0;
+        } else if (score >= 30) {
+            return 1.0;
+        } else {
+            return 0.0;
+        }
+    }
+
+    public boolean isPassing(int score) { return score >= 30; }
+
+    public String getRemark(int score) {
+        if (score < 0 || score > 100) {
+            return "Invalid score";
+        } else if (score >= 80) {
+            return "Excellent";
+        } else if (score >= 70) {
+            return "Good";
+        } else if (score >= 50) {
+            return "Average";
+        } else if (score >= 30) {
+            return "Pass";
+        } else {
+            return "Fail";
+        }
+    }
+}

Student.java

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+public class Student {
+    private String name;
+    private int roll;
+    private String dept;
+    private String batch;
+
+    // DEFAULT CONSTRUCTOR
+    public Student() {}
+
+    // PARAMETERIZED CONSTRUCTOR
+    public Student(String name, int roll, String dept, String batch) {
+        this.name = name;
+        this.roll = roll;
+        this.dept = dept;
+        this.batch = batch;
+    }
+
+    // COPY CONSTRUCTOR
+    public Student(Student student) {
+        this.name = student.getName();
+        this.roll = student.getRoll();
+        this.dept = student.getDept();
+        this.batch = student.getBatch();
+    }
+
+    // GETTERS
+    public String getName() { return name; }
+    public int getRoll() { return roll; }
+    public String getDept() { return dept; }
+    public String getBatch() { return batch; }
+
+    // SETTERS
+    public void setName(String name) { this.name = name; }
+    public void setRoll(int roll) { this.roll = roll; }
+    public void setDept(String dept) { this.dept = dept; }
+    public void setBatch(String batch) { this.batch = batch; }
+}