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- Question
What will be the output of the program?
try { Float f1 = new Float("3.0"); int x = f1.intValue(); byte b = f1.byteValue(); double d = f1.doubleValue(); System.out.println(x + b + d); } catch (NumberFormatException e) /* Line 9 */ { System.out.println("bad number"); /* Line 11 */ }
Options- A. 9.0
- B. bad number
- C. Compilation fails on line 9.
- D. Compilation fails on line 11.
- Correct Answer
- 9.0
ExplanationThe xxxValue() methods convert any numeric wrapper object's value to any primitive type. When narrowing is necessary, significant bits are dropped and the results are difficult to calculate.
Java.lang Class problems
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- 1. What will be the output of the program?
public class ExamQuestion6 { static int x; boolean catch() { x++; return true; } public static void main(String[] args) { x=0; if ((catch() | catch()) || catch()) x++; System.out.println(x); } }
Options- A. 1
- B. 2
- C. 3
- D. Compilation Fails Discuss
Correct Answer: Compilation Fails
Explanation:
Initially this looks like a question about the logical and logical shortcut operators "|" and "||" but on closer inspection it should be noticed that the name of the boolean method in this code is "catch". "catch" is a reserved keyword in the Java language and cannot be used as a method name. Hence Compilation will fail.- 2. What will be the output of the program?
String s = "ABC"; s.toLowerCase(); s += "def"; System.out.println(s);
Options- A. ABC
- B. abc
- C. ABCdef
- D. Compile Error Discuss
Correct Answer: ABCdef
Explanation:
String objects are immutable. The object s above is set to "ABC". Now ask yourself if this object is changed and if so where - remember strings are immutable.Line 2 returns a string object but does not change the originag string object s, so after line 2 s is still "ABC".
So what's happening on line 3? Java will treat line 3 like the following:
s = new StringBuffer().append(s).append("def").toString();
This effectively creates a new String object and stores its reference in the variable s, the old String object containing "ABC" is no longer referenced by a live thread and becomes available for garbage collection.
- 3. What will be the output of the program?
public class NFE { public static void main(String [] args) { String s = "42"; try { s = s.concat(".5"); /* Line 8 */ double d = Double.parseDouble(s); s = Double.toString(d); int x = (int) Math.ceil(Double.valueOf(s).doubleValue()); System.out.println(x); } catch (NumberFormatException e) { System.out.println("bad number"); } } }
Options- A. 42
- B. 42.5
- C. 43
- D. bad number Discuss
Correct Answer: 43
Explanation:
All of this code is legal, and line 8 creates a new String with a value of "42.5". Lines 9 and 10 convert the String to a double and then back again. Line 11 is fun? Math.ceil()'s argument expression is evaluated first. We invoke the valueOf() method that returns an anonymous Double object (with a value of 42.5). Then the doubleValue() method is called (invoked on the newly created Double object), and returns a double primitive (there and back again), with a value of (you guessed it) 42.5. The ceil() method converts this to 43.0, which is cast to an int and assigned to x.- 4. What will be the output of the program?
System.out.println(Math.sqrt(-4D));
Options- A. -2
- B. NaN
- C. Compile Error
- D. Runtime Exception Discuss
Correct Answer: NaN
Explanation:
It is not possible in regular mathematics to get a value for the square-root of a negative number therefore a NaN will be returned because the code is valid.- 5. What will be the output of the program?
String d = "bookkeeper"; d.substring(1,7); d = "w" + d; d.append("woo"); /* Line 4 */ System.out.println(d);
Options- A. wookkeewoo
- B. wbookkeeper
- C. wbookkeewoo
- D. Compilation fails. Discuss
Correct Answer: Compilation fails.
Explanation:
In line 4 the code calls a StringBuffer method, append() on a String object.- 6. What will be the output of the program (in jdk1.6 or above)?
public class BoolTest { public static void main(String [] args) { Boolean b1 = new Boolean("false"); boolean b2; b2 = b1.booleanValue(); if (!b2) { b2 = true; System.out.print("x "); } if (b1 & b2) /* Line 13 */ { System.out.print("y "); } System.out.println("z"); } }
Options- A. z
- B. x z
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- 1. What will be the output of the program?