Thinking in Java Chapter 14

import java.util.*;

abstract class Shape {
	void draw() { System.out.println(this + ".draw()"); }
	abstract public String toString();
}

class Circle extends Shape {
	public String toString() { return "Circle"; }
}

class Square extends Shape {
	public String toString() { return "Square"; }
}

class Triangle extends Shape {
	public String toString() { return "Triangle"; }
}

public class Shapes {
	public static void main(String[] args){
		List<Shape> shapeList = Arrays.asList(new Circle(), new Square(), new Triangle());
		
		for(Shape shape : shapeList)
			shape.draw();
	}
} /* Output:
Circle.draw()
Square.draw()
Triangle.draw()
*/

// Examination of the way the class loader works.
import static net.mindview.util.Print.*;

class Candy {
	static { print("Loading Candy"); }
}

class Gum {
	static { print("Loading Gum"); }
}

class Cookie {
	static { print("Loading Cookie"); }
}

public class SweetShop {
	public static void main(String[] args){
		print("inside main");
		
		new Candy();
		print("After creating Candy");
		
		try {
			Class.forName("Gum");
		} catch(ClassNotFoundException e){
			print("Couldn‘t find Gum");
		}
		print("After Class.forName(\"Gum\")");
		
		new Cookie();
		print("After creating Cookie");
	}
} /* Output:
inside main
Loading Candy
After creating Candy
Loading Gum
After Class.forName("Gum")
Loading Cookie
After creating Cookie
*/

// Testing Class Class.
package Leetcode.DrJava;
import static net.mindview.util.Print.*;

interface HasBatteries {}
interface Waterproof {}
interface Shoots {}

class Toy {
	// Comment out the following default constructor
	// to see NoSuchMethodError from (*1*)
	Toy() {}
	Toy(int i) {}
}

class FancyToy extends Toy implements HasBatteries, Waterproof, Shoots {
	FancyToy() { super(1); }
}

public class ToyTest {
	static void printInfo(Class cc){
		print("Class name: " + cc.getName() + " is interface? [" + cc.isInterface() + "]");
		print("Simple name: " + cc.getSimpleName());
		print("Canonical name: " + cc.getCanonicalName());
	}
	
	public static void main(String[] args){
		Class c = null;
		
		// get the reference of a Class 
		try {
			c = Class.forName("Leetcode.DrJava.FancyToy");
		} catch(ClassNotFoundException e){
			print("Can‘t find FancyToy");
			System.exit(1);
		}		
		printInfo(c);
		
		
		// return the interfaces in "c" Class.
		for(Class face : c.getInterfaces())
			printInfo(face);
		
		
		// return the superclass of the "c" class
		Class up = c.getSuperclass();
		Object obj = null;		
		try {
			// Requires default constructor
			obj = up.newInstance();
		} catch(InstantiationException e){
			print("Cannot instantiate");
			System.exit(1);
		} catch(IllegalAccessException e){
			print("Can‘t access");
			System.exit(1);
		}		
		printInfo(obj.getClass());		
	}
} /* Output:
Class name: Leetcode.DrJava.FancyToy is interface? [false]
Simple name: FancyToy
Canonical name: Leetcode.DrJava.FancyToy
Class name: Leetcode.DrJava.HasBatteries is interface? [true]
Simple name: HasBatteries
Canonical name: Leetcode.DrJava.HasBatteries
Class name: Leetcode.DrJava.Waterproof is interface? [true]
Simple name: Waterproof
Canonical name: Leetcode.DrJava.Waterproof
Class name: Leetcode.DrJava.Shoots is interface? [true]
Simple name: Shoots
Canonical name: Leetcode.DrJava.Shoots
Class name: Leetcode.DrJava.Toy is interface? [false]
Simple name: Toy
Canonical name: Leetcode.DrJava.Toy
*/

FancyToy.class

import java.util.*;

class Initable {
	static final int staticFinal = 47;
	static final int staticFinal2 = ClassInitialization.rand.nextInt(1000);	
	static {
		System.out.println("Initializing Initable");
	}
}

class Initable2 {
	static int staticNonFinal = 147;
	static {
		System.out.println("Initializing Initable2");
	}
}

class Initable3 {
	static int staticNonFinal = 74;
	static {
		System.out.println("Initializing Initable3");
	}
}

public class ClassInitialization {
	public static Random rand = new Random(47);
	
	public static void main(String[] args) throws Exception {
		Class initable = Initable.class;
		System.out.println("After creating Initable ref");
		
		// Does not trigger initialization:
		System.out.println(Initable.staticFinal);
		
		// Does not trigger initialization:
		System.out.println(Initable.staticFinal2);
		
		// Does not trigger initialization:
		System.out.println(Initable2.staticNonFinal);
		
		Class initable3 = Class.forName("Initable3");
		
		System.out.println("After creating Initable3 ref");
		System.out.println(Initable3.staticNonFinal);
	}
} /* Output:
After creating Initable ref
47
Initializing Initable
258
Initializing Initable2
147
Initializing Initable3
After creating Initable3 ref
74
*/