INTERACT w 2 classes OR create COPY of object

Week 4: Writing classes/13A Objects from own classes [i.e. INTERACT w 2 classes OR create COPY of object]

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+Objects formed from their own classes behave like any other objects. 
+That is, objects can be stored in variables and data structures, and their methods can be called in the same way 
+as the methods of objects created from classes that come with Java.
+
+
+-------------------
+
+Objects as method parameters and return values
+
+
+Objects created from their own classes behave as method parameters and 
+return values in the same way as other objects. 
+Methods are passed a reference to a creature, so a method can (as a side effect) modify the creatures it receives as parameters.
+
+
+For example, the class Student and an example of a method that prints student data:
+
+class Student {
+    // ATTRIBUTES
+    private String name;
+    private String studentId;
+    private int studyPoints;
+
+    //CONSTRUCTOR
+    public Student(String name, String studentId, int studyPoints) {
+        this.name = name;
+        this.studentId = studentId;
+        this.studyPoints = studyPoints;
+    }
+ 
+    public String getName() {
+        return name;
+    }
+
+    public String getStudentId() {
+        return studentId;
+    }
+
+    public int getStudyPoints() {
+        return this.studyPoints;
+    }
+        
+    public void setStudyPoints(int studyPoints) {
+        if (studyPoints >= 0) {
+            this.studyPoints = studyPoints;
+        }
+    }
+    
+    public void addPoints(int completionPoints) {
+        if (completionPoints >= 0) {
+            this.studyPoints += completionPoints;
+        }
+    }
+}
+
+
+
+public class TestClass {
+    public static void main(String[] args) {
+        Student sally = new Student("Sally Student", "12345", 154);
+        printStudent(sally);
+    }
+    
+    public static void printStudent(Student student) {
+        System.out.println("Name: " + student.getName());
+        System.out.println("St.id: " + student.getStudentId());
+        System.out.println("Study points: " + student.getStudyPoints());
+    }
+}
+
+TestClass outputs:
+Name: Sally Student
+St.id: 12345
+Study points: 154
+ 
+
+
+
+
+Next, let's define the class Course:
+class Course {
+    private String identifier;
+    private int studyPoints;
+     
+    public Course(String identifier, int studyPoints) {
+        this.identifier = identifier;
+        this.studyPoints = studyPoints;
+    }
+
+    public String getIdentifier() {
+        return identifier;
+    }
+
+    public int getStudyPoints() {
+        return studyPoints;
+    }   
+}
+...and then a method that takes the course and the student as parameters.
+
+The method adds the credits of the course to the credits of the student:
+public class TestClass {
+    public static void main(String[] args) {
+        Student samuel = new Student("Samuel Student", "12345", 154);
+        Course oop = new Course("OOP", 5);
+        
+        addResult(samuel, oop);
+        System.out.println(samuel.getStudyPoints());
+    }
+
+    // NEW METHOD HERE
+    public static void addResult(Student student, Course course) {
+        student.addPoints(course.getStudyPoints());
+    }
+}
+
+Program outputs:
+159
+
+
+
+
+
+
+ 
+
+Of course, the method can also return a new object. 
+The following example creates a new student object by copying the name and student number from the object given as a parameter
+
+public class TestClass {
+    public static void main(String[] args) {
+        Student samantha = new Student("Samantha Student", "12345", 154);
+        Student samantha2 = copy(samantha);
+        
+        System.out.println(samantha2.getName());
+        System.out.println(samantha2.getStudentId());
+        System.out.println(samantha2.getStudyPoints());
+    }
+
+    // FROM INPUT 'student' object
+    // create a 'copy/new student' object
+    // retrieving the input's information
+    public static Student copy(Student student) {
+        Student copy = new Student(student.getName(), 
+            student.getStudentId(), 0);
+        return copy;
+    }
+}
+
+Program outputs:
+Samantha Student
+12345
+0
+
+