question about assigning null to a reference object

I have a class called "Book"

package chapter03;

public class Book {
    String title = "";
    String author = "";
    String subject = "";
    int numberOfPages = 1;

    String getTitle()
    {
        return this.title;
    }
    String getAuthor()
    {
        return this.author;
    }
    String getSubject()
    {
        return this.subject;
    }
    int getPages()
    {
        return this.numberOfPages;
    }
    void setTitle(String t)
    {
        this.title = t;
    }
    void setAuthor(String a)
    {
        this.author = a;
    }
    void setSubject(String s)
    {
        this.subject = s;
    }
    void setPages(int p)
    {
        this.numberOfPages = p;
    }
    void showAll()
    {
        String t = getTitle();
        String a = getAuthor();
        String s = getSubject();
        int p = getPages();
// added the if clause to see if I can prevent a null pointer exception
        if ( t != null && a != null && s != null && p != 0) {
        System.out.print("Book Title: " + t);
        System.out.print(" Author: " + a);
        System.out.print(" Subject: " + s);
        System.out.println(" Pages: " + p);
        }
    }
}

My main program

package chapter03;

public class BookTestDrive {

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Book b = new Book();
        Book c = new Book();
        b.setAuthor("Buce Eckle");
        b.setPages(1123);
        b.setSubject("Java");
        b.setTitle("Thinking in Java 4th Edition");
        b.showAll();

        c.setAuthor("Kathy Sierra & Bert Bates");
        c.setPages(688);
        c.setSubject("Java");
        c.setTitle("Head First Java");
        c.showAll();

        Book d = c;
        d.showAll();
        c = b;
        c.showAll();

        b.setAuthor("Bruce Eckle");
        b.setPages(11212);
        b.setSubject("Javax");
        b.setTitle("Thinking in Java 54th Edition");
        b.showAll();

        c.setAuthor("Kathy Bates & Bert Baccarach");
        c.setPages(688);
        c.setSubject("Javax");
        c.setTitle("Ass Ended Java");
        c.showAll();

        b = c;
        b.showAll();
        c = null;
        c.showAll();
    }
}

When I run the BookTestDrive, my results are what I expect, up until I
call the showAll method on object reference c after I assign it to null.

Book Title: Thinking in Java 4th Edition Author: Buce Eckle Subject:
Java Pages: 1123
Book Title: Head First Java Author: Kathy Sierra & Bert Bates Subject:
Java Pages: 688
Book Title: Head First Java Author: Kathy Sierra & Bert Bates Subject:
Java Pages: 688
Book Title: Thinking in Java 4th Edition Author: Buce Eckle Subject:
Java Pages: 1123
Book Title: Thinking in Java 54th Edition Author: Bruce Eckle Subject:
Javax Pages: 11212
Book Title: Ass Ended Java Author: Kathy Bates & Bert Baccarach Subject:
Javax Pages: 688
Book Title: Ass Ended Java Author: Kathy Bates & Bert Baccarach Subject:
Javax Pages: 688
Exception in thread "main" java.lang.NullPointerException
    at chapter03.BookTestDrive.main(BookTestDrive.java:44)

In order to prevent this exception, I attempted to add the if condition
to the showAll method. However this has not worked. If I assign null
to the c reference object, what are the values of the instance variables
after the reference object is assigned to null? And how can I trap
the NullPointerException. I tried using a try..catch on it

package chapter03;

public class Book {
    String title = "";
    String author = "";
    String subject = "";
    int numberOfPages = 1;
//snip stuff already shown above
    void showAll()
    {
        String t = getTitle();
        String a = getAuthor();
        String s = getSubject();
        int p = getPages();
        try
        {
        System.out.print("Book Title: " + t);
        System.out.print(" Author: " + a);
        System.out.print(" Subject: " + s);
        System.out.println(" Pages: " + p);
        }
        catch (NullPointerException e) {}
    }
}

This would indicate to me that the NullPointerException cannot be
caught? If this is the case then what would I need to test
the instance variables for to ensure that I am not trying to display
something that the JVM will complain about.

I am using jdk1.6, Eclipse 3.3 on Ubuntu Linux if that makes any
difference.

Note: I am using the Head First Java book and am on chapter 3 where
they are talking about the garbage heap. I decided to elaborate a bit
on the sample code to see if I could get a good understanding of it.