public, protected, no set level, private

Week 5: Class hierarchies/05A. Encapsulation and inheriting [++Attribute's 4 visibility levels]

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+The child class inherits all the traits of the parent class. 
+However, the child class does NOT have DIRECT ACCESS to the 'features of the parent class that are protected by the private wrapper'.
+
+If an attempt is made to reference the Name attribute of the Person attribute of the Student class, a translation error occurs:
+
+class Student extends Person {
+    private int studypoints;
+    
+    public Student(String name, String email, int studypoints) {
+        this.name = name;  // HERE
+        this.studypoints = studypoints;
+    }
+}
+ 
+
+However, it would often be convenient to refer to attributes in a child class. 
+But if the private wrapper is removed, the client also has direct access to modify the attributes. 
+So how to solve the dilemma?
+
+
+
+
+============
+
+
+Visibility level protected
+In Java, the problem is solved by a 'third visibility matrix'. 
+In addition to private and public, the visibility wrapper can be set to protected.
+
+A feature protected by the protected wrapper is
+- is AVAILABLE in the CHILD class but
+- is NOT VISIBLE to CLIENTS of the class
+ 
+The table below summarizes all 4 visibility definitions in Java 
+(including the omission of a visibility wrapper as a visibility definition in Java):
+
+Visibility levels in Java
+Level	        Visible within class	Visible within package	Visible within CHILD classes	Visible everywhere
+public	        yes						yes						yes								yes
+protected	    yes						yes						yes								no     <= HERE
+no set level	yes						yes						no								no
+private	        yes						no						no								no
+ 
+
+
+
+Let's now change the definition of the Person class so that the visibility of attributes is 'protected' instead of 'private':
+
+class Person {
+    // 'protected' attribute - subclasses can directly access, clients cant directly access
+    protected String name;
+    protected String email;
+    
+    public Person(String name, String email) {
+        this.name = name;
+        this.email = email; 
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+ 
+    public String getEmail() {
+        return email;
+    }
+
+    public void setEmail(String email) {
+        this.email= email;
+    }  
+}
+ 
+
+Now the Student class can use inherited attributes. 
+The method printStudent refers directly to the attributes defined in the parent class Person.
+
+class Student extends Person {
+    private int studypoints;
+    
+    public Student(String name, String email, int studypoints) {
+        //HERE
+        super(name, email);
+        this.studypoints = studypoints;
+    }
+    
+    public void printStudent() {
+        // Now in the child class we can refer straight to
+        // the attributes defined in the parent class
+        System.out.println("Name" + name);
+        System.out.println("Email:" + email);
+        System.out.println("Studypoints: " + studypoints);
+    }
+
+    public int getStudypoints() {
+        return studypoints;
+    }
+
+    public void setStudypoints(int studypoints) {
+        this.studypoints = studypoints;
+    } 
+}
+
+
+
+
+