inheritance demo: client class to perform operations

CodingBlocks Training/Day16/clientInheritance.java

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+package Lecture16;
+
+public class clientInheritance {
+
+	public static void main(String[] args) {
+
+		// part 1
+		parentInheritance obj = new parentInheritance();
+
+		System.out.println(obj.age);
+		obj.read();
+		obj.sing();
+
+		System.out.println("===========================================");
+		// part2
+		parentInheritance obj2 = new ChildInheritance(); // parent can hold child reference
+
+		System.out.println(obj2.age);  // dynamic polymorphism
+		// exceptional case(parent holding child): in case of variable, obj2 will show parent value
+		// if it was method, it would be overwritten 
+
+		System.out.println(obj2.rollno);
+//		System.out.println(obj2.name); // name cannot be resolved or is not a field
+
+		// compiler will check name variable in parent class i.e parentInheritance here,
+		// as name is not present in parent class, compiler will throw compile time error.
+		// new ChildInheritance() - this part is checked by JRE 
+		// parentInheritance obj2 - this part is checked by compiler
+
+		obj2.sing();
+		obj2.read();
+//		obj2.write(); // The method write() is undefined for the type parentInheritance
+
+		// similar to above, here write() is not present in parent class as obj2 
+		// reference is hold by parent class, and compiler will check the presence of write()
+		// method in parent class during compilation, as it don't find there, it gives error
+		// to access child class write(), you need to hold obj2 reference by child class itself here
+
+		System.out.println("===========================================");
+		// part3
+
+		ChildInheritance obj3 = new ChildInheritance();
+
+		System.out.println(obj3.age); // here age will also be overwritten
+		// unlike above exceptional case with variable, here reference is of same class as right side
+		// here - child holds child reference so it is overwritten
+
+		System.out.println(obj3.name);
+		System.out.println(obj3.rollno);
+
+		obj3.sing();
+		obj3.read();
+		obj3.write();
+	}
+
+}
+
+
+/* output:
+40
+Inside parent read method
+Inside parent sing menthod
+===========================================
+40
+7
+Inside parent sing menthod
+Inside child read method
+===========================================
+20
+Trishna
+7
+Inside parent sing menthod
+Inside child read method
+Inside child write method
+*/