CS 61B, Spring, 2006, Hilfinger
1. [10 points] Indicate the outcome of executing each of the following (one of “compilation error”,
“runtime error”, or whatever is printed). In each case, briefly justify your answer:
Code Result
a.
String s = "Hello ";
String s2 = s; "not equal" – the addition creates a new
s = s + "there"; string, so s and s2 point to different things.
if( s == s2 )
System.out.println ( "equal" );
else
System.out.println( "not equal" );
b.
class Test {
public void greet () { compilation error – cannot call an instance
System.out.println( "Hello!" ); method from a static method
}
public static void main (String[] args ) {
greet();
}
}
c.
class Thing {
int x; "equal" – Thing's equals method is called
public Thing( int x ) { and returns true
this.x = x;
}
public boolean equals( Object p ) {
return x == ((Thing) p).x;
}
public static void main(String[] args ) {
Object p1 = new Thing(3),
p2 = new Thing(3);
if( p1.equals(p2) )
System.out.println("equal");
else
System.out.println("not equal");
}
}
