diff --git a/Chapter7/theoretical/Using_abstract_classes_2.java b/Chapter7/theoretical/Using_abstract_classes_2.java
new file mode 100644
index 0000000..50dfcfd
--- /dev/null
+++ b/Chapter7/theoretical/Using_abstract_classes_2.java
@@ -0,0 +1,73 @@
+package theoretical;
+
+abstract class TwoDShapes{
+	
+	private double width;
+	private double height;
+	private String name;
+	
+	public TwoDShapes() {
+		
+		width = height = 0.0;
+		name = "none";
+	}
+	
+	TwoDShapes(double w, double h, String n){
+		width = w; 
+		height = h;
+		name = n;
+	}
+	
+	TwoDShapes(double x, String n){
+		width = height = x;
+		name = n;
+	}
+	
+	// Construct an object from an object.
+	TwoDShapes(TwoDShapes ob){
+		width = ob.width;
+		height = ob.height;
+		name = ob.name;
+	}
+	
+	
+	double getWidth() {
+		return width;
+	}
+	
+	double getHeight() {return height;}
+	void setWidth(double w) { width = w;}
+	void setHeight(double h) {height = h;}
+	String getName() {return name;}
+	void showDimension() {
+		System.out.println("Width and height are " + width + " and " + height);
+	}
+	
+	// Now, area() is abstract.
+	abstract double area();
+}
+
+
+class Triangle extends TwoDShapes{
+	
+	private String style;
+	
+	public Triangle() {
+		// TODO Auto-generated constructor stub
+		super();
+		style = "none";
+	}
+	
+}
+
+
+public class Using_abstract_classes_2 {
+
+	public static void main(String[] args) {
+		// TODO Auto-generated method stub
+		
+		
+
+	}
+
+}
diff --git a/Chapter7/theoretical/Using_super_to_call_superclass_constructor.java b/Chapter7/theoretical/Using_super_to_call_superclass_constructor.java
new file mode 100644
index 0000000..9e3e923
--- /dev/null
+++ b/Chapter7/theoretical/Using_super_to_call_superclass_constructor.java
@@ -0,0 +1,83 @@
+package theoretical;
+
+class TwoDShaper{
+	
+	private double width;
+	private double height;
+	
+	public TwoDShaper(double w, double h) {
+		// TODO Auto-generated constructor stub
+	}
+	
+	double getWidth() {
+		return width;
+	}
+	
+	double getHeight() {
+		return height;
+	}
+	
+	void setWidth(double w) {
+		width = w;
+	}
+	
+	void setHeight(double h) {
+		height = h;
+	}
+	
+	void showDim() {
+		
+		System.out.println("Width and height are " + width + " and " + height);
+	}
+	
+}
+
+
+class Triangular extends TwoDShaper{
+	
+	private String style;
+	
+	public Triangular(String s, double w, double h) {
+		super(w, h);
+		
+		style = s;
+	}
+	
+	double area() {
+		return getWidth() * getHeight() / 2;
+	}
+	
+	void showStyle() {
+		System.out.println("Triangle is " + style);
+	}
+}
+
+public class Using_super_to_call_superclass_constructor {
+
+	public static void main(String[] args) {
+		
+		Triangular t1 = new Triangular("filled", 4.0, 4.0);
+		Triangular t2 = new Triangular("outlined", 8.0, 12.0);
+		
+		System.out.println("Info for t1: ");
+		t1.showStyle();
+		t1.showDim();
+		System.out.println("Area is " + t1.area());
+		
+		System.out.println();
+		
+		System.out.println("Info for t2: ");
+		t2.showStyle();
+		t2.showDim();
+		System.out.println("Area is " + t2.area());		
+		
+		System.out.println();
+		
+		System.out.println("Info for t2: ");
+		t2.showStyle();
+		t2.showDim();
+		System.out.println("Area is " + t2.area());
+
+	}
+
+}
diff --git a/Chapter7/theoretical/Using_super_to_call_superclass_constructor_2.java b/Chapter7/theoretical/Using_super_to_call_superclass_constructor_2.java
new file mode 100644
index 0000000..1efe849
--- /dev/null
+++ b/Chapter7/theoretical/Using_super_to_call_superclass_constructor_2.java
@@ -0,0 +1,122 @@
+package theoretical;
+
+class TwoDShaper_2{
+	
+	private double width;
+	private double height;
+	private String title;
+	
+	public TwoDShaper_2(double w, double h) {
+		// TODO Auto-generated constructor stub
+	}
+	
+	public TwoDShaper_2() {
+		// TODO Auto-generated constructor stub
+	}
+	
+	TwoDShaper_2(double width, double height, String title){
+		
+		this.width = width;
+		this.height = height;
+		this.title = title;
+		
+	}
+	
+	
+	double getWidth() {
+		return width;
+	}
+	
+	double getHeight() {
+		return height;
+	}
+	
+	void setWidth(double w) {
+		width = w;
+	}
+	
+	void setHeight(double h) {
+		height = h;
+	}
+	
+	void showDim() {
+		
+		System.out.println("Width and height are " + width + " and " + height);
+	}
+	
+	String showTitle() {
+		return title;
+	}
+	
+}
+
+
+class Triangular_2 extends TwoDShaper_2{
+	
+	private String style;
+	
+	public Triangular_2() {
+		// TODO Auto-generated constructor stub
+	}
+	
+	public Triangular_2(String s, double w, double h) {
+		super(w, h);
+		
+		style = s;
+	}
+	
+	Triangular_2(String style, String title, double width, double height){
+		
+		super(width, height, title);
+		
+		this.style = style;
+		
+	}
+	
+	double area() {
+		return getWidth() * getHeight() / 2;
+	}
+	
+	void showStyle() {
+		System.out.println("Triangle is " + style);
+	}
+	
+	String showTitle() {
+		
+		return showTitle();
+		
+	}
+	
+}
+
+
+public class Using_super_to_call_superclass_constructor_2 {
+
+	public static void main(String[] args) {
+		// TODO Auto-generated method stub
+		Triangular_2 t1 = new Triangular_2("filled", 4.0, 4.0);
+		Triangular_2 t2 = new Triangular_2("outlined", 8.0, 12.0);
+		Triangular_2 t3 = new Triangular_2("Slovenly", "Classy", 8.0, 9.0);
+		
+		System.out.println("Info for t1: ");
+		t1.showStyle();
+		t1.showDim();
+		System.out.println("Area is " + t1.area());
+		
+		System.out.println();
+		
+		System.out.println("Info for t2: ");
+		t2.showStyle();
+		t2.showDim();
+		System.out.println("Area is " + t2.area());		
+		
+		System.out.println();
+		
+		System.out.println("Info for t3: ");
+		t3.showStyle();
+		t3.showDim();
+		t3.showTitle();
+		System.out.println("Area is " + t3.area());
+	}
+
+}
diff --git a/Chapter7/theoretical/Using_super_to_call_superclass_constructor_3.java b/Chapter7/theoretical/Using_super_to_call_superclass_constructor_3.java
new file mode 100644
index 0000000..e974c2a
--- /dev/null
+++ b/Chapter7/theoretical/Using_super_to_call_superclass_constructor_3.java
@@ -0,0 +1,127 @@
+package theoretical;
+
+
+class TwoDShaper_3{
+	
+	private double width;
+	private double height;
+	private String title;
+	
+	public TwoDShaper_3(double w, double h) {
+		// TODO Auto-generated constructor stub
+	}
+	
+	public TwoDShaper_3() {
+		// TODO Auto-generated constructor stub
+	}
+	
+	TwoDShaper_3(double width, double height, String title){
+		
+		this.width = width;
+		this.height = height;
+		this.title = title;
+		
+	}
+	
+	
+	double getWidth() {
+		return width;
+	}
+	
+	double getHeight() {
+		return height;
+	}
+	
+	void setWidth(double w) {
+		width = w;
+	}
+	
+	void setHeight(double h) {
+		height = h;
+	}
+	
+	void showDim() {
+		
+		System.out.println("Width and height are " + width + " and " + height);
+	}
+	
+	String showTitle() {
+		return title;
+	}
+	
+}
+
+
+
+class Triangular_3 extends TwoDShaper_3{
+	
+	private String style;
+	
+	public Triangular_3() {
+		// TODO Auto-generated constructor stub
+	}
+	
+	public Triangular_3(String s, double w, double h) {
+		super(w, h);
+		
+		style = s;
+	}
+	
+	Triangular_3(String style, String title, double width, double height){
+		
+		super(width, height, title);
+		
+		this.style = style;
+		
+	}
+	
+	double area() {
+		return getWidth() * getHeight() / 2;
+	}
+	
+	void showStyle() {
+		System.out.println("Triangle is " + style);
+	}
+	
+	String showTheTitle() {
+		
+		return showTitle();
+		
+	}
+	
+}
+
+
+
+public class Using_super_to_call_superclass_constructor_3 {
+
+	public static void main(String[] args) {
+		// TODO Auto-generated method stub
+		Triangular_3 t1 = new Triangular_3("filled", 4.0, 4.0);
+		Triangular_3 t2 = new Triangular_3("outlined", 8.0, 12.0);
+		Triangular_3 t3 = new Triangular_3("Slovenly", "Classy", 8.0, 9.0);
+		
+		System.out.println("Info for t1: ");
+		t1.showStyle();
+		t1.showDim();
+		System.out.println("Area is " + t1.area());
+		
+		System.out.println();
+		
+		System.out.println("Info for t2: ");
+		t2.showStyle();
+		t2.showDim();
+		System.out.println("Area is " + t2.area());		
+		
+		System.out.println();
+		
+		System.out.println("Info for t3: ");
+		t3.showStyle();
+		t3.showDim();
+		t3.showTitle();
+		t3.showTheTitle();
+		System.out.println("Area is " + t3.area());
+
+	}
+
+}
diff --git a/Chapter7/theoretical/Using_super_to_call_superclass_constructor_4.java b/Chapter7/theoretical/Using_super_to_call_superclass_constructor_4.java
new file mode 100644
index 0000000..e58cc11
--- /dev/null
+++ b/Chapter7/theoretical/Using_super_to_call_superclass_constructor_4.java
@@ -0,0 +1,138 @@
+package theoretical;
+
+
+class TwoDShaper_4{
+	
+	private double width;
+	private double height;
+	private String title;
+	
+	public TwoDShaper_4(double w, double h) {
+		width = w;
+		height = h;
+	}
+	
+	public TwoDShaper_4() {
+		// TODO Auto-generated constructor stub
+	}
+	
+	TwoDShaper_4(double width, double height, String title){
+		
+		this.width = width;
+		this.height = height;
+		this.title = title;
+		
+	}
+	
+	
+	double getWidth() {
+		return width;
+	}
+	
+	double getHeight() {
+		return height;
+	}
+	
+	void setWidth(double w) {
+		width = w;
+	}
+	
+	void setHeight(double h) {
+		height = h;
+	}
+	
+	void showDim() {
+		
+		System.out.println("Width and height are " + width + " and " + height);
+	}
+	
+	String showTitle() {
+		return title;
+	}
+	
+}
+
+
+class Triangular_4 extends TwoDShaper_4{
+	
+	private String style;
+	
+	public Triangular_4() {
+		// TODO Auto-generated constructor stub
+	}
+	
+	public Triangular_4(String s, double w, double h) {
+		super(w, h);
+		
+		style = s;
+	}
+	
+	Triangular_4(String style, String title, double width, double height){
+		
+		super(width, height, title);
+		
+		this.style = style;
+		
+	}
+	
+	double area() {
+		return getWidth() * getHeight() / 2;
+	}
+	
+	void showStyle() {
+		System.out.println("Triangle is " + style);
+	}
+	
+	String showTheTitle() {
+		
+		return showTitle();
+		
+	}
+	
+}
+
+
+
+public class Using_super_to_call_superclass_constructor_4 {
+
+	public static void main(String[] args) {
+		// TODO Auto-generated method stub
+		Triangular_4 t0 = new Triangular_4();
+		Triangular_4 t1 = new Triangular_4("filled", 4.0, 4.0);
+		Triangular_4 t2 = new Triangular_4("outlined", 8.0, 12.0);
+		Triangular_4 t3 = new Triangular_4("Slovenly", "Classy", 8.0, 9.0);
+		
+		System.out.println("Info for t0: ");
+		t0.showStyle();
+		t0.setHeight(9);
+		t0.setWidth(3);
+		t0.showDim();
+		t0.showTitle();
+		t0.showTheTitle();
+		System.out.println("Area is " + t0.area());
+		
+		System.out.println();
+		
+		System.out.println("Info for t1: ");
+		t1.showStyle();
+		t1.showDim();
+		System.out.println("Area is " + t1.area());
+		
+		System.out.println();
+		
+		System.out.println("Info for t2: ");
+		t2.showStyle();
+		t2.showDim();
+		System.out.println("Area is " + t2.area());		
+		
+		System.out.println();
+		
+		System.out.println("Info for t3: ");
+		t3.showStyle();
+		t3.showDim();
+		t3.showTitle();
+		t3.showTheTitle();
+		System.out.println("Area is " + t3.area());
+	}
+
+}
diff --git a/Chapter7/theoretical/Using_super_to_call_superclass_constructor_5.java b/Chapter7/theoretical/Using_super_to_call_superclass_constructor_5.java
new file mode 100644
index 0000000..99fdeae
--- /dev/null
+++ b/Chapter7/theoretical/Using_super_to_call_superclass_constructor_5.java
@@ -0,0 +1,144 @@
+package theoretical;
+
+class TwoDShaper_5{
+	
+	private double width;
+	private double height;
+	String title;
+	
+	public TwoDShaper_5(double w, double h) {
+		width = w;
+		height = h;
+	}
+	
+	public TwoDShaper_5() {
+		// TODO Auto-generated constructor stub
+	}
+	
+	TwoDShaper_5(double width, double height, String title){
+		
+		this.width = width;
+		this.height = height;
+		this.title = title;
+		
+	}
+	
+	
+	double getWidth() {
+		return width;
+	}
+	
+	double getHeight() {
+		return height;
+	}
+	
+	void setWidth(double w) {
+		width = w;
+	}
+	
+	void setHeight(double h) {
+		height = h;
+	}
+	
+	void showDim() {
+		
+		System.out.println("Width and height are " + width + " and " + height);
+	}
+	
+	String showTitle() {
+		return title;
+	}
+	
+	void showTitle_2() {
+		System.out.println("Triangle is also " + title);
+	}
+	
+}
+
+
+class Triangular_5 extends TwoDShaper_5{
+	
+	private String style;
+	
+	public Triangular_5() {
+		// TODO Auto-generated constructor stub
+	}
+	
+	public Triangular_5(String s, double w, double h) {
+		super(w, h);
+		
+		style = s;
+	}
+	
+	Triangular_5(String style, String title, double width, double height){
+		
+		super(width, height, title);
+		
+		this.style = style;
+		
+	}
+	
+	double area() {
+		return getWidth() * getHeight() / 2;
+	}
+	
+	void showStyle() {
+		System.out.println("Triangle is " + style);
+	}
+	
+	String showTheTitle() {
+		
+		return showTitle();
+		
+	}
+	
+	void showTheTitle_2() {
+		System.out.println("Triangle is also " + super.title);
+	}
+	
+}
+
+
+public class Using_super_to_call_superclass_constructor_5 {
+
+	public static void main(String[] args) {
+		Triangular_5 t0 = new Triangular_5();
+		Triangular_5 t1 = new Triangular_5("filled", 4.0, 4.0);
+		Triangular_5 t2 = new Triangular_5("outlined", 8.0, 12.0);
+		Triangular_5 t3 = new Triangular_5("Slovenly", "Classy", 8.0, 9.0);
+		
+		System.out.println("Info for t0: ");
+		t0.showStyle();
+		t0.setHeight(9);
+		t0.setWidth(3);
+		t0.showDim();
+		t0.showTitle();
+		t0.showTheTitle();
+		System.out.println("Area is " + t0.area());
+		
+		System.out.println();
+		
+		System.out.println("Info for t1: ");
+		t1.showStyle();
+		t1.showDim();
+		System.out.println("Area is " + t1.area());
+		
+		System.out.println();
+		
+		System.out.println("Info for t2: ");
+		t2.showStyle();
+		t2.showDim();
+		System.out.println("Area is " + t2.area());		
+		
+		System.out.println();
+		
+		System.out.println("Info for t3: ");
+		t3.showStyle();
+		t3.showDim();
+		t3.showTitle_2();
+		t3.showTheTitle_2();
+		System.out.println("Area is " + t3.area());
+
+	}
+
+}
diff --git a/Chapter7/theoretical/Using_super_to_call_superclass_constructor_6.java b/Chapter7/theoretical/Using_super_to_call_superclass_constructor_6.java
new file mode 100644
index 0000000..a0f932b
--- /dev/null
+++ b/Chapter7/theoretical/Using_super_to_call_superclass_constructor_6.java
@@ -0,0 +1,151 @@
+package theoretical;
+
+
+class TwoDShaper_6{
+	
+	private double width;
+	private double height;
+	String title;
+	
+	public TwoDShaper_6(double w, double h) {
+		width = w;
+		height = h;
+	}
+	
+	public TwoDShaper_6() {
+		// TODO Auto-generated constructor stub
+	}
+	
+	TwoDShaper_6(double width, double height, String title){
+		
+		this.width = width;
+		this.height = height;
+		this.title = title;
+		
+	}
+	
+	
+	double getWidth() {
+		return width;
+	}
+	
+	double getHeight() {
+		return height;
+	}
+	
+	void setWidth(double w) {
+		width = w;
+	}
+	
+	void setHeight(double h) {
+		height = h;
+	}
+	
+	void showDim() {
+		
+		System.out.println("Width and height are " + width + " and " + height);
+	}
+	
+	String showTitle() {
+		return title;
+	}
+	
+	void showTitle_2() {
+		System.out.println("Triangle is also " + title);
+	}
+	
+}
+
+
+class Triangular_6 extends TwoDShaper_6{
+	
+	private String style;
+	
+	public Triangular_6() {
+		// TODO Auto-generated constructor stub
+	}
+	
+	public Triangular_6(String s, double w, double h) {
+		super(w, h);
+		
+		style = s;
+	}
+	
+	Triangular_6(String style, String title, double width, double height){
+		
+		super(width, height, title);
+		
+		this.style = style;
+		
+	}
+	
+	double area() {
+		return getWidth() * getHeight() / 2;
+	}
+	
+	void showStyle() {
+		System.out.println("Triangle is " + style);
+	}
+	
+	String showTheTitle() {
+		
+		return showTitle();
+		
+	}
+	
+	void showTheTitle_2() {
+		System.out.println("Triangle is also " + super.title);   // super is redundant here.
+	}
+	
+	void showTheTitle_3() {
+		System.out.println("Triangle is also " + title);
+	}
+	
+}
+
+
+public class Using_super_to_call_superclass_constructor_6 {
+
+	public static void main(String[] args) {
+		
+		Triangular_6 t0 = new Triangular_6();
+		Triangular_6 t1 = new Triangular_6("filled", 4.0, 4.0);
+		Triangular_6 t2 = new Triangular_6("outlined", 8.0, 12.0);
+		Triangular_6 t3 = new Triangular_6("Slovenly", "Classy", 8.0, 9.0);
+		
+		System.out.println("Info for t0: ");
+		t0.showStyle();
+		t0.setHeight(9);
+		t0.setWidth(3);
+		t0.showDim();
+		t0.showTitle();
+		t0.showTheTitle();
+		System.out.println("Area is " + t0.area());
+		
+		System.out.println();
+		
+		System.out.println("Info for t1: ");
+		t1.showStyle();
+		t1.showDim();
+		System.out.println("Area is " + t1.area());
+		
+		System.out.println();
+		
+		System.out.println("Info for t2: ");
+		t2.showStyle();
+		t2.showDim();
+		System.out.println("Area is " + t2.area());		
+		
+		System.out.println();
+		
+		System.out.println("Info for t3: ");
+		t3.showStyle();
+		t3.showDim();
+		t3.showTitle_2();
+		t3.showTheTitle_2();
+		t3.showTheTitle_3();
+		System.out.println("Area is " + t3.area());
+		
+	}
+
+}