OCPJP Simulation Test 12

12

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Question: What is the output of the following program?

  1 import java.io.*;
  2 class Pet implements Serializable {}
  3 public class PetStore implements Serializable {
  4   private String name;
  5   private int year;
  6   private Pet pet;
  7   public String getName() {return this.name;}
  8   public void setName(String name) {this.name = name;}
  9   public int getYear() { return year;}
 10   public void setYear(int year) { this.year = year;}
 11   public Pet getPet() { return pet;}
 12   public void setPet(Pet pet) {this.pet = pet;}
 13 
 14   public static void main(String[] args) {
 15     try(ObjectOutputStream out = new ObjectOutputStream(
 16       new BufferedOutputStream(new FileOutputStream("pet.dat")));
 17       ObjectInputStream in = new ObjectInputStream(
 18       new BufferedInputStream(new FileInputStream("pet.dat")))) {
 19       PetStore pet = new PetStore();
 20       out.writeObject(pet);
 21       pet = (PetStore)in.readObject();
 22       System.out.println(pet.getName()+pet.getYear());
 23     }}}

Choice:
A. null0
B. null
C. blank  line
D. The code does not compile because of line 15-18
E. The code does not compile because of line 20
F. The code does not compile because of line 21
G. None of the above



Next Question

Answer: D, E, F

Explain: resources declared in try-with-resources block are automatically closed when exiting the block, however, you still need to handle checked Exceptions. new ObjectOutputStream() and new ObjectInputStream() can throw IOException, new FileOutputStream() and new FileInputStream() can throw FileNotFoundException, readObject() and writeObject() can throw IOException. Besides, cast Object to PetStore will throw ClassNotFoundException.
If line 14 is change to public static void main(String[] args) throws IOExeption, FileNotFoundException, ClassNotFoundException { , the answer will be G. The code compiles, but throws java.io.EOFException at runtime. The reason is new ObjectOutputStream() will write a header to the file, which new ObjectInputStream() will first check. Before output stream flush the contents out, in already read and get EOFException.

Study:  Use BufferedReader, BufferedWriter, File, FileReader, FileWriter, FileInputStream, FileOutputStream, ObjectOutputStream, ObjectInputStream, and PrintWriter in the java.iopackage.