Download Java Quiz: Identifying Valid Java Statements and more Exercises Computer Science in PDF only on Docsity!
Signature _____________________ CSE 11 Name ________________________
Quiz 3
cs11f ____ Fall 2009 Student ID ____________________
This quiz is to be taken by yourself with closed books, closed notes, no calculators.
What is the output produced by this program? (Hint: Draw Stack Frames!)
public class Mystery
public static void main( String[] args )
Mystery ref = new Mystery();
System.out.println( ref.mystery( 5 ) );
private int mystery( int a )
int b = a + 3;
if ( b >= 6 )
System.out.println( b );
b = a + mystery( a - 1 );
System.out.println( a );
else
System.out.println( "Whoa!" );
b = a;
System.out.println( a );
return b;
(over)
Output
Given the following definitions:
And the following variable definitions:
private Puppy puppy; private Kitty kitty; private Speakable speakable;
Indicate which are valid Java statements. Consider each statement executed sequentially in the order it appears.
A) Invalid Java statement – Compiler Error B) Valid Java statement – No Compiler Error
kitty = new Kitty(); _______
puppy = new Puppy(); _______
puppy.speak(); _______
puppy.wag(); _______
puppy.sleep( 1000 ); _______
kitty.speak(); _______
kitty.wag(); _______
kitty.sleep( 2000 ); _______
speakable = kitty; _______
speakable.speak(); _______
speakable.wag(); _______
speakable = puppy; _______
speakable.speak(); _______
speakable.sleep( 3000 ); _______
puppy = kitty; _______
speakable = new Speakable(); _______
public interface Speakable { public String speak(); }
public class Puppy implements Speakable { private static final String PUPPY_SPEAK = "Bark";
public Puppy() { // ctor initialization here }
public String speak() { return PUPPY_SPEAK; }
public void sleep( int time ) { // puppy sleeps for time seconds } }
public class Kitty implements Speakable { private static final String KITTY_SPEAK = "Meow";
public Kitty() { // ctor initialization here }
public String speak() { return KITTY_SPEAK; }
public void wag() { // kitty wags its tail } }
Hint: What does the compiler know about any reference variable at compile time (vs. run time)?
