A. Boolean exists=Directory.exists （“prefs”）；
B. Boolean exists=（new File（“prefs”））.isDir（）；
C. Boolean exists=（new Directory（“prefs”））.exists（）；
D. Boolean exists=（new File（“prefs”））.isDirectory（）；
E. Boolean exists=true； Try{ Directory d = new Directory（“prefs”）； } catch （FileNotFoundException e） { exists = false； }
您可能感兴趣的试卷
你可能感兴趣的试题
class super {
public int getLength（） {return 4；}
}
public class Sub extends Super {
public long getLength（） {return 5；}
public static void main （Stringargs） {
super sooper = new Super （）；
Sub sub = new Sub（）；
System.out.printIn（
sooper.getLength（）+ “，” + sub.getLength（） }；
}
What is the output？（）
A. 4， 4
B. 4， 5
C. 5， 4
D. 5， 5
E. The code will not compile.
A. The default constructor initializes method variables.
B. The compiler always creates a default constructor for every class.
C. The default constructor invokes the no-parameter constructor of the superclass.
D. The default constructor initializes the instance variables declared in the class.
E. When a class has only constructors with parameters， the compiler does not create a default constructor.
public class ArrayTest {
public static void main （Stringargs） {
float f1， f2；
f1 = new float [10]；
f2 = f1；
System.out.printIn （“f2[0]=” + f2[0]）；
}
}
What is the result？（）
A. It prints f2[0] = 0.0
B. It prints f2[0] = NaN
C. An error at line 5 causes compile to fail.
D. An error at line 6 causes compile to fail.
E. An error at line 6 causes an exception at runtime.
ClassOne.java
package com.abc.pkg1；
public class ClassOne {
private char var = ‘a‘；
char getVar（） {return var；}
}
ClassTest.java
package com.abc.pkg2；
import com.abc.pkg1.ClassOne；
public class ClassTest extends ClassOne {
public static void main（Stringargs） {
char a = new ClassOne（）.getVar（）；
char b = new ClassTest（）.getVar（）；
}
}
What is the result？（）
A. Compilation will fail.
B. Compilation succeeds and no exceptions are thrown.
C. Compilation succeeds but an exception is thrown at line 5 in ClassTest.java.
D. Compilation succeeds but an exception is thrown at line 6 in ClassTest.java.
A. Public
B. Private
C. Protected
D. Transient
E. No access modifier is required
public class Mycircle {
public double radius；
public double diameter；
public void setRadius（double radius）
this.radius = radius；
this.diameter= radius * 2；
}
public double getRadius（） {
return radius；
}
Which statement is true？（）
A. The Mycircle class is fully encapsulated.
B. The diameter of a given MyCircle is guaranteed to be twice its radius.
C. Lines 6 and 7 should be in a synchronized block to ensure encapsulation.
D. The radius of a MyCircle object can be set without affecting its diameter.
A. An inner class may be declared as static.
B. An anonymous inner class can be declared as public.
C. An anonymous inner class can be declared as private.
D. An anonymous inner class can extend an abstract class.
E. An anonymous inner class can be declared as protected.
AnInterface is an interface.
AnAdapter0 is a non-abstract， non-final class with a zero argument constructor.
AnAdapter1 is a non-abstract， non-final class without a zero argument constructor， but with a constructor that takes one int argument.
Which two construct an anonymous inner class？ （）
A. AnAdapter1 aa=new AnAdapter1（）{}
B.AnAdapter0 aa=new AnAdapter0（）{}
C. AnAdapter0 aa=new AnAdapter0（5）{}
D. AnAdapter1 aa=new AnAdapter1（5）{}
E.AnInterface a1=new AnInterface（5）{}
class A {
public byte getNumber （） {
return 1；
}
}
class B extends A {
public short getNumber（） {
return 2；
}
public static void main （String args） {
B b = new B （）；
System.out.printIn（b.getNumber（））
}
}
What is the result？（）
A. Compilation succeeds and 1 is printed.
B. Compilation succeeds and 2 is printed.
C. An error at line 8 causes compilation to fail.
D. An error at line 14 causes compilation to fail.
E. Compilation succeeds but an exception is thrown at line 14.
A. An anonymous class can be declared as static.
B. A static inner class cannot be a static member of the outer class.
C. A static inner class does not require an instance of the enclosing class.
D. Instance members of a static inner class can be referenced using the class name of the static inner class.
最新试题
What is the result？（）
What is the result？（）
Which three changes should be made to adapt this class to be used safely by multiple threads？（）
What is the result？（）
What is the result？（）
Given a class whose instances， when found in a collection of objects， are sorted by using the compareTo（） method， which two statements are true？（）
What can be a result？（）
Which statement is true？（）
Which statement is true？（）
What is the appropriate definition of the hashCode method in class Person？（）