A. false
B. default
C. _object
D. a-class

A. New BufferedInputStream（“in.txt”）；
B. New BufferedInputStream（new File（“in.txt”））；
C. New BufferedInputStream（Writer（“in.txt”））；
D. New BufferedInputStream（new Writer（“in.txt”））；
E. New BufferedInputStream（new InputStream（“in.txt”））；
F. New BufferedInputStream（new FileInputStream（“in.txt”））；

A. OutputStream out=new FileOutputStream（“file.txt”）；
B. OutputStream out=new FileOutputStream（“file.txt”， “append”）；
C. FileOutputStream out=new FileOutputStream（“file.txt”， true）；
D. FileOutputStream out=new FileOutputStream（new file（“file.txt”））；
E. OutputStream out=new FileOutputStream（new File（“file.txt”）true）；

A. InputStream in=new FileReader（“file.txt”）；
B. InputStream in=new FileInputStream（“file.txt”）；
C. InputStream in=new InputStreamFileReader （“file.txt”， “read”）；
D. FileInputStream in=new FileReader（new File（“file.txt”））；
E. FileInputStream in=new FileInputStream（new File（“file.txt”））；

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；  }

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.

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.

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

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.