public interface A { String DEFAULT_GREETING = “Hello World”; public void method1(); } A programmer wants to create an interface called B that has A as its parent. Which interface declaration is correct?()
第1题:
interface Playable {
void play();
}
interface Bounceable {
void play();
}
interface Rollable extends Playable, Bounceable {
Ball ball = new Ball("PingPang");
}
class Ball implements Rollable {
private String name;
public String getName() {
return name;
}
public Ball(String name) {
this.name = name;
}
public void play() {
ball = new Ball("Football");
System.out.println(ball.getName());
}
}
这个错误不容易发现。
错。"interface Rollable extends Playable, Bounceable"没有问题。interface 可继承多个
interfaces,所以这里没错。问题出在interface Rollable 里的"Ball ball = new Ball("PingPang");"。
任何在interface 里声明的interface variable (接口变量,也可称成员变量),默认为public static
final。也就是说"Ball ball = new Ball("PingPang");"实际上是"public static final Ball ball = new
Ball("PingPang");"。在Ball 类的Play()方法中,"ball = new Ball("Football");"改变了ball 的
reference,而这里的ball 来自Rollable interface,Rollable interface 里的ball 是public static final
的,final 的object 是不能被改变reference 的。因此编译器将在"ball = new Ball("Football");"
这里显示有错。
第2题:
Which three demonstrate an “is a” relationship?()
第3题:
A programmer needs to create a logging method that can accept an arbitrary number of arguments. For example, it may be called in these ways: logIt(”log message 1 “); logIt(”log message2”,”log message3”); logIt(”log message4”, “log message5”, “log message6); Which declaration satisfies this requirement?()
第4题:
Which is a method of the MouseMotionListener interface?()
第5题:
Which the two demonstrate an “is a” relationship?()
第6题:
Which two demonstrate an “is a” relationship?()
第7题:
1. interface A { public void aMethod(); } 2. interface B { public void bMethod(); } 3. interface C extends A,B { public void cMethod(); } 4. class D implements B { 5. public void bMethod() { } 6. } 7. class E extends D implements C { 8. public void aMethod() { } 9. public void bMethod() { } 10. public void cMethod() { } 11. } What is the result?()
第8题:
public interface Person { } public class Employee extends Person { }
public interface Shape { } public class Employee extends Shape { }
public interface Color { } public class Employee extends Color { }
public class Species { } public class Animal (private Species species;)
interface Component { } Class Container implements Component ( Private Component[ ] children; )
第9题:
Public void mouseMoved(MouseEvent)
Public boolean mouseMoved(MouseEvent)
Public void mouseMoved(MouseMotionEvent)
Public boolean MouseMoved(MouseMotionEvent)
Public boolean mouseMoved(MouseMotionEvent)
第10题:
0
1
2
3
第11题:
public void logIt(String * msgs)
public void logIt(String [] msgs)
public void logIt(String... msgs)
public void logIt(String msg1, String msg2, String msg3)
第12题:
public class Employee extends Info implements Data { public void load() { /*do something*/ } }
public class Employee implements Info extends Data { public void load() { /*do something*/ } }
public class Employee extends Info implements Data { public void load() { /*do something */ } public void Info.load() { /*do something*/ } }
public class Employee implements Info extends Data { public void Data.load() { /*dsomething */ } public void load() { /*do something */ } }
public class Employee implements Info extends Data { public void load() { /*do something */ } public void Info.load(){ /*do something*/ } }
public class Employee extends Info implements Data{ public void Data.load() { /*do something*/ } public void Info.load() { /*do something*/ } }
第13题:
A programmer needs to create a logging method that can accept an arbitrary number of arguments.Forexample,it may be called in these ways: logIt("log message 1"); logIt("log message 2”,”log message 3"); logIt("log message 4","log message 5","log message 6"); Which declaration satisfies this requirement()?
第14题:
interface Data { public void load(); } abstract class Info { public abstract void load(); } Which class correctly uses the Data interface and Info class?()
第15题:
Which method must be defined by a class implementing the java.lang.Runnable interface? ()
第16题:
现有: interface Data {public void load();} abstract class Info {public abstract void load();} 下列类定义中正确使用Data和Info的是哪项?()
第17题:
interface A { public int getValue() } class B implements A { public int getValue() { return 1; } } class C extends B { // insert code here } Which three code fragments, inserted individually at line 15, make use of polymorphism?()
第18题:
现有: 1. interface Animal { 2. void eat(); 3. } 4. 5. // insert code here 6. 7. public class HouseCat implements Feline { 8. public void eat() { } 9. } 和以下三个接口声明: interface Feline extends Animal { } interface Feline extends Animal { void eat(); } interface Feline extends Animal { void eat() { } } 分别插入到第 5 行,有多少行可以编译?()
第19题:
public interface B extends A {}
public interface B implements A {}
public interface B instanceOf A {}
public interface B inheritsFrom A {}
第20题:
void run()
public void run()
public void start()
void run(int priority)
public void run(int priority)
public void start(int priority)
第21题:
public interface Person {} Public class Employee extends Person {}
public interface Shape {} public interface Rectangle extends Shape {}
public interface Color {} public class Shape { private Color color; }
public class Species {} public class Animal { private Species species; }
interface Component {} Class Container implements Component {private Component [] children;
第22题:
public class X { } public class Y extends X { }
public interface Shape { } public interface Rectangle extends Shape{ }
public interface Color { } public class Shape { private Color color; }
public interface Species { } public class Animal { private Species species; }
public class Person { } public class Employee { public Employee(Person person) { }
interface Component { } class Container implements Component { private Component[] children; }
第23题:
Cat is-a Animal
Cat is-a Jumper
Dog is-a Animal
Dog is-a Jumper
Cat has-a Animal
Beagle has-a Tail
Beagle has-a Jumper