ResilientSpring · ResilientSpring · Oct 5, 2023 · Oct 1, 2023 · Oct 1, 2023 · Oct 1, 2023
diff --git a/Chapter7/IncompatibleRef.java b/Chapter7/IncompatibleRef.java
@@ -1,38 +1,37 @@
-import java.awt.PrintGraphics;
-
 // This will not compile 
 class X {
+
 	int a;
-	
+
 	X(int i) {
 		a = i;
 	}
 }

 class Y {
-	int a ;
-
-	Y(int i){
+
+	int a;
+
+	Y(int i) {
 		a = i;
 	}
-
-}

+}

 public class IncompatibleRef {

 	public static void main(String[] args) {
 		// TODO Auto-generated method stub
-		
+
 		X x = new X(10);
-		
+
 		X x2;
-		
+
 		Y y = new Y(5);
-		
-		x2 = x;  // Ok, both of same type. 
-		
-		x2 = y; // Error, not of same type. 
+
+		x2 = x; // Ok, both of same type.
+
+		x2 = y; // Error, not of same type.

 	}


diff --git a/Chapter7/theoretical/SupSubRef.java b/Chapter7/theoretical/SupSubRef.java
@@ -0,0 +1,48 @@
+package theoretical;
+
+//A superclass reference can refer to a subclass object. 
+
+class X {
+
+	int a;
+
+	public X(int i) {
+		a = i;
+	}
+}
+
+
+class Y extends X {
+
+	int b;
+
+	public Y(int i, int j) {
+
+		super(j);
+		b = i;
+	}
+}
+
+
+public class SupSubRef {
+
+	public static void main(String[] args) {
+
+		X x = new X(10);
+		X x2;
+		Y y = new Y(5, 6);
+
+		x2 = x; // OK, both of same type.
+		System.out.println("X2.a: " + x2.a);
+		System.out.println("x.a: " + x.a);
+
+		x2 = y; // still ok because Y is derived from X.
+		System.out.println("X2.a: " + x2.a);
+
+		// X references know only about X members
+		x2.a = 19; // OK
+// 		x2.b = 27;  // Error, X does not have a b member. 
+
+	}
+
+}
diff --git a/Chapter8/Interface/Interfaces_Can_Be_Extended.java b/Chapter8/Interface/Interfaces_Can_Be_Extended.java
@@ -0,0 +1,51 @@
+package Interface;
+
+// One interface can extend another.
+interface A{
+
+	void meth1();
+	void meth2();
+}
+
+// B now includes meth1() and meth2() - it adds meth3().
+interface B extends A{  // B inherits A.
+	void meth3();
+}
+
+// This class must implement all of A and B
+class MyClass implements B{
+
+	@Override
+	public void meth1() {
+		// TODO Auto-generated method stub
+		System.out.println("Implement meth1(). ");
+	}
+
+	@Override
+	public void meth2() {
+		// TODO Auto-generated method stub
+		System.out.println("Implement meth2(). ");
+	}
+
+	@Override
+	public void meth3() {
+		// TODO Auto-generated method stub
+		System.out.println("Implement meth3(). ");
+	}
+}
+
+
+public class Interfaces_Can_Be_Extended {
+
+	public static void main(String[] args) {
+		// TODO Auto-generated method stub
+
+		MyClass obMyClass = new MyClass();
+
+		obMyClass.meth1();
+		obMyClass.meth2();
+		obMyClass.meth3();
+
+	}
+
+}
diff --git a/Chapter8/Interface/Using_Interface_References.java b/Chapter8/Interface/Using_Interface_References.java
@@ -0,0 +1,98 @@
+package Interface;
+
+// An interface specifies what to do, not how to do.
+interface Seriess{
+	int getNext();
+	void reset();
+	void setStart(int x);
+}
+
+class ByTwoss implements Seriess{
+
+	int start;
+	int value;
+
+	public ByTwoss() {
+		start = 0;
+		value = 0;
+	}
+
+	@Override
+	public int getNext() {
+		value += 2;
+		return value;
+	}
+
+	@Override
+	public void reset() {
+		value = start;
+
+	}
+
+	@Override
+	public void setStart(int x) {
+		// TODO Auto-generated method stub
+		start = x;
+		value = x;
+	}
+
+}
+
+
+class ByThreess implements Seriess{
+
+	int start;
+	int value;
+
+	public ByThreess() {
+		start = 0;
+		value = 0;
+	}
+
+	@Override
+	public int getNext() {
+
+		value += 3;
+
+		return value;
+	}
+
+	@Override
+	public void reset() {
+		// TODO Auto-generated method stub
+		value = start;
+	}
+
+	@Override
+	public void setStart(int x) {
+		// TODO Auto-generated method stub
+		start = x;
+		value = x;
+	}
+
+}
+
+
+public class Using_Interface_References {
+
+	public static void main(String[] args) {
+
+		ByTwoss twoOb = new ByTwoss();
+		ByThreess threeOb = new ByThreess();
+		Seriess ob;
+
+		for (int i = 0; i < 5; i++) {
+
+			ob = twoOb;
+
+			System.out.println("Next ByTwos value is " + ob.getNext());
+
+			ob = threeOb;
+
+			System.out.println("Next ByThrees value is " + ob.getNext());
+
+		}
+
+	}
+
+}