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
*BA protected method in class x can be overridden by any subclass of x
*CA private static method can be called only with in other static method in class x
*DA non-static public final method in class x can be overridden in any subclass x
*EA public static method in class x can be called by a subclass of x without explicitly referencing *the class x
*FA 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
*
*finalprotectedprivate abstractstatic
*/
// 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?
*
*AValue is :8
*BCompilation fails
*CValue is :12
*DValue is :-12
*EThe Code is runs with no output
*FAn 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
*BThe code demonstrates polymorphism
*CThe ownerName variable breaks encapsulation
*DThe cardID and limit variables break polymorphism
*EThe 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 ?
*
*
*Apeep
*Bbark
*Cmove
*DCompilation fails
*EAn 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?
*
*
*Ainsert a call to this() in the Car Constructor
*Binsert a call to this() in the MeGo Constructor
*Cinsert a call to super() in the MeGo Constructor
*Dinsert a call to super(vin) in the MeGo Constructor
*Echange the wheelCount variable in Car protected
*Fchange line 3 in the MeGo class to super wheelCount =3;
*/
// Answerhttp://www.agoit.com/images/smiles/icon_biggrin.gif E
/** * * @author yaoyuan */10interface A { public int getValue();}11class B implements A{12public int getValue(){return 1;}13}14class C extends B{1516}
/**
*What three code fragments inserted individually at line 15, make use of polymorphism?
*
*
*A public void add(C c){c.getValue();}
*Bpublic void add(B b){b.getValue();}
*Cpublic void add(A a){a.getValue();}
*Dpublic void add(A a, B b){a.getValue();}
*Epublic void add(C c1, C c2){c1.getValue();}
*/
// Answer : B C D
/** * * @author yaoyuan */11certkiller = new ReallyBigObject();12//more code here13certkiller = 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?
*
*
*ASystem.gc();
*BRuntime.gc();
*CSystem.freeMemory();
*DRuntime.getRuntime() growHeap()
*ERuntime.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
*BThe JAR file is located at $JAVA_HOME/jre/lib/ext/myLib.jar
*CThe JAR file is located at /foo/myLib.jar and a classpath environment variable is set that includes
*/foo/myLib.jar/Paper.class
*DThe JAR file is located at /foo/myLib.jar and a classpath environment variable is set that includes
* /foo/myLib.jar
*EThe JARfile is located at /foo/myLib.jar and the Book class is compiled using javac -cp */foo/myLib.jar Book.java
*
*FThe JAR file is located at /foo/myLib.jar and the Book class is compiled using javac -d **/foo/myLib.jar Book.java
*
*GThe 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 */11class Certkiller{12Boochy booch;13public Certkiller(){booch = new Boochy(this);}14}1516class Boochy{17Certkiller smooch;18public Boochy(Certkiller s){smoothy = s;}19}and the statements:21public static void main(String[] args){22Certkiller snoog = new Certkiller();23snoog = null;24//more code here25}
/**
*Which statement is true about the object referenced by snoog,smooch and booch immediately after line 23 *executes?
*
*
*ANone of these objects are eligible for garbage collection
*Bonly the object referenced by booch is eligible for garbage collection
*Conly the object referenced by snoog is eligible for garbage collection
*Donly the object referenced by smooch is eligible for garbage collection
*EThe Objects referenced by smooch and booch are eligible for garbage collection
*/
// Answer : E
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