SCJP认证试题(三)

/**
*
* @author yaoyuan
*/

/**
*Which three statements are true?(choose three)
*
*A      A final method in class x can be abstract if and only if x is abstract
*B A protected method in class x can be overridden by any subclass of x
*C A private static method can be called only with in other static method in class x
*D A non-static public final method in class x can be overridden in any subclass x
*E A public static method in class x can be called by a subclass of x without explicitly referencing * the class x
*F A method with the same signature as a private final method in class x can be implement entered in * a subclass of x
*/

// Answer : B E F



/**
*
* @author yaoyuan
*/

/**
*Replace two of the Modifiers that appear in the Single class to make the code compile
*
*Note:Three Modifiers will not be used and four midifiers in the code will remain unchanged
*
*/

/**
	Code
*/

public class Single{
	/*private*/ /*static*/ Single instance;
	
	/*public*/ /*static*/ Single getInstance(){
		if(instance == null)
			instance = create();
			return instance;
	}
	
	/*private*/ Single(){
	
	}
	
	/*protected*/ Single create(){
		return new Single();
	}
}

class SingleSub extends Single{
	
}

/**
* Modifiers
*
* final protected private abstract static
*/



// Answer :
//
// public class Single{
// private static Single instance;
//
// public static Single getInstance(){
// if(instance == null)
// instance = create();
// return instance;
// }
// protected Single(){
//
// }
//
// static Single create(){
// return new Single();
// }
// }
//
// class SingleSub extends Single{
//
// }
//
//

 /**
 *
 * @author yaoyuan
 */
public class SimpleCalc{
	public int value;
	
	public void calculate(){
		value += 7;
	}
}

public class Multicalc extends SimpleCalc{
	
	public void calculate(){
		value -= 3;
	}
	
	public void calculate(int multiplier){
		calculate();
		super.calculate();
		value *= multiplier;
	}
	
	public static void main(String[] args){
		Multicalc calculator = new Multicalc();
		calculator.calculate(2);
		System.out.println("Value is :" + calculator.value);
	}

}

/**
*What is the result?
*
*A Value is :8
*B Compilation fails
*C Value is :12
*D Value is :-12
*E The Code is runs with no output
*F An Exception is thrown at runtime
*/

// Answer : A

 /**
 *
 * @author yaoyuan
 */
public class CertkillerCard{

	private String cardID;
	private Integer limit;
	public String ownerName;

	public void setCardInformation(String cardID, String ownerName, Integer limit){
		this.cardID = cardID;
		this.limit = limit;
		this.ownerName = ownerName;
	}

}

/**
*Which statement is true?
*
*
*A      The class is fully encapsulated
*B The code demonstrates polymorphism
*C The ownerName variable breaks encapsulation
*D The cardID and limit variables break polymorphism
*E The setCardInformation method breaks encapsulation
*/

// Answer : C

/**
* encapsulated   封装
* polymorphism   多态
* demonstrates   展示
*/

  /**
 *
 * @author yaoyuan
 */
class Animal{
	public String noise(){
		return "peep";
	}
}

class Dog extends Animal{
	public String noise(){
		return "back";
	}
}

class Cat extends Animal{
	public String noise(){
		return "move";
	}
}

...................
...................
...................

Animal animal = new Dog();
Cat cat = (Cat)animal;
System.out.println(Cat.noise());

/**
*What is the result ?
*
*
*A peep
*B bark
*C move
*D Compilation fails
*E An exception is thrown at runtime
*/

// Answer : E


/**
*
*Cat cat = (Cat)animal;    这行出错了，Dog不能强制转换成Cat对象
*
*/

 /**
 *
 * @author yaoyuan
 */
public class Car{
	private int wheelCount;
	private String vin;
	
	public Car(String vin){
		this.vin = vin;
		this.wheelCount = 4;
	}
	
	public String extend(){
		return "zoom zoom";
	}
	
	public String getInfo(){
		return "VIN:" + vin + "wheels:" + wheelCount;
	}
}

public class MeGo extends Car{
	public MeGo(String vin){
		this.wheelCount = 3;
	}
}

/**
* What two must the programmer do to oerrect the compilation errors?
*
*
*A insert a call to this() in the Car Constructor
*B insert a call to this() in the MeGo Constructor
*C insert a call to super() in the MeGo Constructor
*D insert a call to super(vin) in the MeGo Constructor
*E change the wheelCount variable in Car protected
*F change line 3 in the MeGo class to super wheelCount =3;
*/

// Answer E

  /**
 *
 * @author yaoyuan
 */

10	interface A { public int getValue();}
11	class B implements A{
12		public int getValue(){return 1;}
13	}		
14	class C extends B{	
15		[insert code here]
16	}

/**
*What three code fragments inserted individually at line 15, make use of polymorphism?
*
*
*A      public void add(C c){c.getValue();}
*B public void add(B b){b.getValue();}
*C public void add(A a){a.getValue();}
*D public void add(A a, B b){a.getValue();}
*E public void add(C c1, C c2){c1.getValue();}
*/

// Answer : B C D

 /**
 *
 * @author yaoyuan
 */

11	certkiller = new ReallyBigObject();
12	//more code here
13	certkiller = null;
14	/*insert code here*/

/**
*Which statement should be placed at line 14 to suggest that the virtual machine expend effort tow and recycling the memory used by the Object certkiller?
*
*
*A System.gc();
*B Runtime.gc();
*C System.freeMemory();
*D Runtime.getRuntime() growHeap()
*E Runtime.getRuntime() freeMemory()
*/

// Answer : A


/**
*
* @author yaoyuan
*/


/**
*A developer is creating a class Book, that needs to access class Paper,The Paper class is deployed in a JAR named myLib.jar.
*Which three, taken independently, will allow the developer to use the Paper class while compiling the Book class? (choose three)
*
*
*A      The JAR file is located at $JAVA_HOME/jre/classes/myLib.jar
*B The JAR file is located at $JAVA_HOME/jre/lib/ext/myLib.jar
*C The JAR file is located at /foo/myLib.jar and a classpath environment variable is set that includes
* /foo/myLib.jar/Paper.class
*D The JAR file is located at /foo/myLib.jar and a classpath environment variable is set that includes
* /foo/myLib.jar
*E The JAR file is located at /foo/myLib.jar and the Book class is compiled using javac -cp * /foo/myLib.jar Book.java
*
*F The JAR file is located at /foo/myLib.jar and the Book class is compiled using javac -d * * /foo/myLib.jar Book.java
*
*G The JAR file is located at /foo/myLib.jar and the Book class is compiled using javac -classpath * /foo/myLib.jar Book.java
*/

// Answer : B D G

 /**
 *
 * @author yaoyuan
 */
11	class Certkiller{
12		Boochy booch;
13		public Certkiller(){booch = new Boochy(this);}
14	}
15	
16	class Boochy{
17		Certkiller smooch;
18		public Boochy(Certkiller s){smoothy = s;}
19	}
and the statements:
21	public static void main(String[] args){
22		Certkiller snoog = new Certkiller();
23		snoog = null;
24		//more code here
25	}

/**
*Which statement is true about the object referenced by snoog,smooch and booch immediately after line 23 *executes?
*
*
*A None of these objects are eligible for garbage collection
*B only the object referenced by booch is eligible for garbage collection
*C only the object referenced by snoog is eligible for garbage collection
*D only the object referenced by smooch is eligible for garbage collection
*E The Objects referenced by smooch and booch are eligible for garbage collection
*/

// Answer : E