class, constructor

Week 4: Writing classes/03A Writing a class: file contents

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+A class is defined by the class identifier. 
+As stated earlier, all code in Java must be written inside classes. 
+However, not all the code that is written is directed at the objects that are created from the class. 
+
+
+In Java, the class name must be exactly the same as the file name. 
+Specifically, a file must have a public class defined by its name. 
+
+For example, the file Car.java must have a class definition of
+public class Car
+ 
+...and from the file OwnFineClass.java definition
+public class OwnFineClass
+
+ 
+
+You can write MORE THAN 1 CLASS in the SAME FILE, but ONLY 1 can be PUBLIC. 
+The others are initialized without the public attribute.
+
+A class has different features. Features can be public or private. 
+When an object is created from a class, the client of the object has direct access to the public features. 
+The client in this context is the program code through which the entity is accessed 
+(it does not mean, for example, the program user or any other physical person).
+
+
+
+
+
+
+
+====================================================================================================================================================
+
+
+
+
+
+Attributes
+Let's start by looking at the attributes of the class (note the two t's). 
+An attribute is a variable of an object. 
+They are therefore used to define the information content of the objects that make up the class. 
+Each object in a class has its own values for all the attributes defined in the class.
+
+
+
+As an example, consider a class that models a student. 
+The class has three attributes: name, student number and credits:
+
+public class Student {
+    // Attributes are usually defined at the start of the class
+    String name;
+    String studentId;
+    int studyPoints;
+}
+
+
+ 
+
+ATTRIBUTES are thus defined inside the class, but OUTSIDE ANY METHODS.
+Typically, attribute variables are assigned values in the CONSTRUCTOR based on PARAMETERS YOU PASS IN. 
+
+
+
+
+So let's write a constructor for the Student class:
+public class Student {
+    // Attributes are usually defined at the start of the class
+    String name; 
+    String studentId; 
+    int studyPoints;
+	
+    // Constructor
+    public Student(String n, String id, int sp) {
+        name = n;
+        studentId = id;
+        studyPoints = sp;
+    }
+}
+ 
+
+
+
+Now new student objects can be created using the new operator:
+public class Testclass {
+    public static void main(String[] args) {
+        Student sally = new Student("Sally Student", "12345", 10);
+        Student sam = new Student("Sam Student", "99999", 35);
+    }
+}
+