Declarations and Access Control Questions

• Java top-level class access modifiers and loop stepping: does this code compile, and if so what prints? import java.util.*; public class NewTreeSet2 extends NewTreeSet { public static void main(String[] args) { NewTreeSet2 t = new NewTreeSet2(); t.count(); } } protected class NewTreeSet { // illegal: top-level classes cannot be protected void count() { for (int x = 0; x < 7; x++, x++) { System.out.print(" " + x); } } }
• Java local classes, casting through Object, and type safety at runtime: what is printed? public class Test { public static void main(String[] args) { class Foo { public int i = 3; } Object o = (Object) new Foo(); Foo foo = (Foo) o; System.out.println("i = " + foo.i); } }
• Java array references and default initialization: determine f2[0] after assigning f2 = f1. public class ArrayTest { public static void main(String[] args) { float f1[], f2[]; f1 = new float[10]; f2 = f1; System.out.println("f2[0] = " + f2[0]); } }
• Java method-local static variables are not allowed: what happens when a method declares "static int i" locally? public class Test { public int aMethod() { static int i = 0; // illegal: static not allowed in local context i++; return i; } public static void main(String args[]) { Test test = new Test(); test.aMethod(); int j = test.aMethod(); System.out.println(j); } }
• Java method overriding and covariant returns: can a subclass change Integer to Long in an override? class Super { public Integer getLength() { return new Integer(4); } } public class Sub extends Super { public Long getLength() { return new Long(5); } public static void main(String[] args) { Super sooper = new Super(); Sub sub = new Sub(); System.out.println(sooper.getLength().toString() + "," + sub.getLength().toString()); } }
• Java constructor chaining: subclass must invoke a superclass constructor; what is the outcome here? class Super { public int i = 0; public Super(String text) { i = 1; } } class Sub extends Super { public Sub(String text) { i = 2; } public static void main(String args[]) { Sub sub = new Sub("Hello"); System.out.println(sub.i); } }
• Java inheritance and constructors — what exact output is printed? class Base { Base() { System.out.print("Base"); } } public class Alpha extends Base { public static void main(String[] args) { new Alpha(); // Line 12 new Base(); // Line 13 } } Predict the combined standard output produced by running main().
• Java methods and overriding — what happens when a subclass attempts to override a final method? class A { final public int GetResult(int a, int b) { return 0; } } class B extends A { public int GetResult(int a, int b) { return 1; } } public class Test { public static void main(String args[]) { B b = new B(); System.out.println("x = " + b.GetResult(0, 1)); } } Choose the correct outcome.