Java quiz questions

Which of the following is true?

public class A implements Comparable {
  final int a;
  A(final int a) {
    this.a = a;
  }
  public int compareTo(A that) {
    return this.a - that.a;
  }
  public static void main(String[] args) {
    A a1 = new A(1);
    A a2 = new A(2);
    System.out.println(a1 > a2);
  }
}

1. member variable can not be final

2. constructor parameter cannot be final

3. compareTo must take Object as parameter

4. operator > is not defined for type A

5. nothing is wrong with this code

Which of the following is true?

public static final class Class {
  static final int id = 1;
  Class() {
  }
  static public int id() {
    return id;
  }
}

1. class cannot be instantiated because of non-public constructor

2. class cannot be final

3. class cannot be static

4. class cannot be named Class because it is a reserved keyword

5. nothing is wrong with this code

Which of the following is true?

public class Main {
  public static void main() {
    System.out.println("1234".length());
  }
}

1. The code will print "4"

2. The code will print "1234"

3. The code won't compile

4. The code will fail at run time

Which of the following is true?

public final class Main {
  static final String s = "hello";
  public void main(String[] args) {
    System.out.println(s);
  }
}

1. The code will print "hello"

2. The code won't compile

3. The code will fail at run time

Which of the following is true?

public class A {
  public String foo() {
    return "a";
  }
}
public class B extends A {
  public String foo() {
    return "b";
  }
}
public class Main {
  public static void main(String[] args) {
    A a = (A) new B();
    System.out.println(a.foo());
  }
}

1. The code will print "a"

2. The code will print "b"

3. The code won

4. The code will fail at run time

Which of the following is true?

public class Base {
  public String toString() {
    return "Base";
  }
}
public class Derived extends Base {
  public String toString() {
    return "Derived";
  }
}
public class Main {
  public static void main(String[] args) {
    Base b = new Derived();
    System.out.println(b);
  }
}

1. The code won't compile

2. The code will fail at run time

3. The code will print "Base"

4. The code will print "Derived"

Which of the following is true?

public interface I {
  public void method();
}
public abstract class C implements I {
  private C() {
  }
  public static C getInstance() {
    return new C();
  }
  public void method() {
  }
}

1. class C cannot be instantiated because of private constructor

2. class C cannot be instantiated because it is abstract

3. method getInstance() cannot be static

4. there is nothing wrong with this code

What of following will happen?

public class A {
  public void main(String[] args) {
    A[] array = new A[10];
    System.out.println(array.length);
  }
}

1. The code will not compile

2. There will be a run time error

3. The code will print 0

4. The code will print 10

Which of the following is true?

package a;
class A {
  public void foo() {
     System.out.println("a");
  }
}
package b;
import a.A;
public class B extends A {
  public void foo() {
    System.out.println("b");
  }
  public static void main(String[] args) {
    new B().foo();
  }
}

1. The code won't compile

2. There will be a run time error

3. The code will print "a"

4. The code will print "b"

What will be printed?

int a = 10;
System.out.println(a + ~a);

1. -1

2. 0

3. 1

4. 10

5. 20

What will be printed?

String s1 = "a";
String s2 = s1;
s1 += "b";
System.out.println(s2);

1. a

2. b

3. ab

What will be printed?

String s1 = "a";
String s2 = "a";
System.out.println(s1 == s2);

1. true

2. false

What will be printed?

int a = 1;
a += ++a * a;
System.out.println(a);

1. 1

2. 2

3. 4

4. 5

5. 6

What will be the result of running this code?

public class Test {
  static boolean printAndReturn(boolean value) {
    System.out.println(value);
    return value;
  }
  public static void main(String[] args) {
    if (printAndReturn(false) && printAndReturn(true)) {
      System.out.println(true);
    } else {
      System.out.println(false);
    }
  }
}

1. output: false true false

2. output: false false

3. output: true false true

4. compilation error

5. run time error

What will be printed?

String s1 = new String("a");
String s2 = new String("a");
System.out.println(s1 == s2);

1. true

2. false

What will be the result of executing this code?

String s = null;
if ((s != null) || (!s.isEmpty())) {
  System.out.println(s);
} else {
  System.out.println("the string is null");
}

1. "the string is null"

2. "null"

3. NullPointerException

4. compilation error

What will be printed?

byte b = (byte) 128;
b >>>= 1;
System.out.println(b);

1. 128

2. 64

3. -128

4. -64

What will be printed?

int a = -1;
a = a >>> 1;
System.out.println(a);

1. -1

2. 0

3. 1

4. 2147483647

5. -2147483647

What will be printed?

int a = -1;
a = a >> 1;
System.out.println(a);

1. 0

2. 1

3. -1

4. 2147483647

5. -2147483647

What will be printed?

boolean value = 
  Double.POSITIVE_INFINITY == Double.POSITIVE_INFINITY;
System.out.println(value);

1. true

2. false