Exercise: Java Lang Class

Questions for: Java Lang Class

What will be the output of the program? 
public class WrapTest 
{
    public static void main(String [] args) 
    {
        int result = 0;
        short s = 42;
        Long x = new Long("42");
        Long y = new Long(42);
        Short z = new Short("42");
        Short x2 = new Short(s);
        Integer y2 = new Integer("42");
        Integer z2 = new Integer(42);

        if (x == y) /* Line 13 */
            result = 1;
        if (x.equals(y) ) /* Line 15 */
            result = result + 10;
        if (x.equals(z) ) /* Line 17 */
            result = result + 100;
        if (x.equals(x2) ) /* Line 19 */
            result = result + 1000;
        if (x.equals(z2) ) /* Line 21 */
            result = result + 10000;

        System.out.println("result = " + result);
    }
}
A:
result = 1
B:
result = 10
C:
result = 11
D:
result = 11010
Answer: B

Line 13 fails because == compares reference values, not object values. Line 15 succeeds because both String and primitive wrapper constructors resolve to the same value (except for the Character wrapper). Lines 17, 19, and 21 fail because the equals() method fails if the object classes being compared are different and not in the same tree hierarchy.

📖
📝
💬
👁️
What will be the output of the program? 
String x = new String("xyz");
String y = "abc";
x = x + y;
How many String objects have been created?
A:
2
B:
3
C:
4
D:
5
Answer: C

Line 1 creates two, one referred to by x and the lost String "xyz". Line 2 creates one (for a total of three). Line 3 creates one more (for a total of four), the concatenated String referred to by x with a value of "xyzabc".

📖
📝
💬
👁️ 
public class Myfile 
{ 
    public static void main (String[] args) 
    {
        String biz = args[1]; 
        String baz = args[2]; 
        String rip = args[3]; 
        System.out.println("Arg is " + rip); 
    } 
}
Select how you would start the program to cause it to print: Arg is 2
A:
java Myfile 222
B:
java Myfile 1 2 2 3 4
C:
java Myfile 1 3 2 2
D:
java Myfile 0 1 2 3
Answer: C

Arguments start at array element 0 so the fourth arguement must be 2 to produce the correct output.

📖
📝
💬
👁️
Which of the following are valid calls to Math.max?
  1. Math.max(1,4)
  2. Math.max(2.3, 5)
  3. Math.max(1, 3, 5, 7)
  4. Math.max(-1.5, -2.8f)
A:
1, 2 and 4
B:
2, 3 and 4
C:
1, 2 and 3
D:
3 and 4
Answer: A

(1), (2), and (4) are correct. The max() method is overloaded to take two arguments of type int, long, float, or double.

(3) is incorrect because the max() method only takes two arguments.

📖
📝
💬
👁️
Which of the following would compile without error?
A:
int a = Math.abs(-5);
B:
int b = Math.abs(5.0);
C:
int c = Math.abs(5.5F);
D:
int d = Math.abs(5L);
Answer: A

The return value of the Math.abs() method is always the same as the type of the parameter passed into that method.

In the case of A, an integer is passed in and so the result is also an integer which is fine for assignment to "int a".

The values used in B, C & D respectively are a double, a float and a long. The compiler will complain about a possible loss of precision if we try to assign the results to an "int".

📖
📝
💬
👁️
Ad Slot (Above Pagination)
Quiz