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- Question
What will be the output of the program?
public class Test { public static void main(String [] args) { signed int x = 10; for (int y=0; y<5; y++, x--) System.out.print(x + ", "); } }
Options- A. 10, 9, 8, 7, 6,
- B. 9, 8, 7, 6, 5,
- C. Compilation fails.
- D. An exception is thrown at runtime.
- Correct Answer
- Compilation fails.
ExplanationThe word "signed" is not a valid modifier keyword in the Java language. All number primitives in Java are signed. Hence the Compilation will fails.
Language Fundamentals problems
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- 1. What will be the output of the program?
public class TestDogs { public static void main(String [] args) { Dog [][] theDogs = new Dog[3][]; System.out.println(theDogs[2][0].toString()); } } class Dog { }
Options- A. null
- B. theDogs
- C. Compilation fails
- D. An exception is thrown at runtime Discuss
Correct Answer: An exception is thrown at runtime
Explanation:
The second dimension of the array referenced by theDogs has not been initialized. Attempting to access an uninitialized object element (System.out.println(theDogs[2][0].toString());) raises a NullPointerException.- 2. What will be the output of the program?
public class CommandArgsTwo { public static void main(String [] argh) { int x; x = argh.length; for (int y = 1; y <= x; y++) { System.out.print(" " + argh[y]); } } }and the command-line invocation is> java CommandArgsTwo 1 2 3
Options- A. 0 1 2
- B. 1 2 3
- C. 0 0 0
- D. An exception is thrown at runtime Discuss
Correct Answer: An exception is thrown at runtime
Explanation:
An exception is thrown because at some point in (System.out.print(" " + argh[y]);), the value of x will be equal to y, resulting in an attempt to access an index out of bounds for the array. Remember that you can access only as far as length - 1, so loop logical tests should use x < someArray.length as opposed to x < = someArray.length.- 3. What will be the output of the program, if this code is executed with the command line:
> java F0091 world
public class F0091 { public void main( String[] args ) { System.out.println( "Hello" + args[0] ); } }
Options- A. Hello
- B. Hello Foo91
- C. Hello world
- D. The code does not run. Discuss
Correct Answer: The code does not run.
Explanation:
Option D is correct. A runtime error will occur owning to the main method of the code fragment not being declared static:Exception in thread "main" java.lang.NoSuchMethodError: main
The Java Language Specification clearly states: "The main method must be declared public, static, and void. It must accept a single argument that is an array of strings."
- 4. What will be the output of the program?
public class X { public static void main(String [] args) { String names [] = new String[5]; for (int x=0; x < args.length; x++) names[x] = args[x]; System.out.println(names[2]); } }and the command line invocation is> java X a b
Options- A. names
- B. null
- C. Compilation fails
- D. An exception is thrown at runtime Discuss
Correct Answer: null
Explanation:
The names array is initialized with five null elements. Then elements 0 and 1 are assigned the String values "a" and "b" respectively (the command-line arguments passed to main). Elements of names array 2, 3, and 4 remain unassigned, so they have a value of null.- 5. What will be the output of the program?
public class CommandArgsThree { public static void main(String [] args) { String [][] argCopy = new String[2][2]; int x; argCopy[0] = args; x = argCopy[0].length; for (int y = 0; y < x; y++) { System.out.print(" " + argCopy[0][y]); } } }and the command-line invocation is> java CommandArgsThree 1 2 3
Options- A. 0 0
- B. 1 2
- C. 0 0 0
- D. 1 2 3 Discuss
Correct Answer: 1 2 3
Explanation:
In argCopy[0] = args;, the reference variable argCopy[0], which was referring to an array with two elements, is reassigned to an array ( args) with three elements.- 6. What will be the output of the program?
public class CommandArgs { public static void main(String [] args) { String s1 = args[1]; String s2 = args[2]; String s3 = args[3]; String s4 = args[4]; System.out.print(" args[2] = " + s2); } }and the command-line invocation is> java CommandArgs 1 2 3 4
Options- A. args[2] = 2
- B. args[2] = 3
- C. args[2] = null
- D. An exception is thrown at runtime. Discuss
Correct Answer: An exception is thrown at runtime.
Explanation:
An exception is thrown because in the code String s4 = args[4];, the array index (the fifth element) is out of bounds. The exception thrown is the cleverly named ArrayIndexOutOfBoundsException.- 7. In the given program, how many lines of output will be produced?
public class Test { public static void main(String [] args) { int [] [] [] x = new int [3] [] []; int i, j; x[0] = new int[4][]; x[1] = new int[2][]; x[2] = new int[5][]; for (i = 0; i < x.length; i++) { for (j = 0; j < x[i].length; j++) { x[i][j] = new int [i + j + 1]; System.out.println("size = " + x[i][j].length); } } } }
Options- A. 7
- B. 9
- C. 11
- D. 13
- E. Compilation fails Discuss
Correct Answer: 11
Explanation:
The loops use the array sizes (length).It produces 11 lines of output as given below.
D:\Java>javac Test.java D:\Java>java Test size = 1 size = 2 size = 3 size = 4 size = 2 size = 3 size = 3 size = 4 size = 5 size = 6 size = 7
Therefore, 11 is the answer.
- 8. Which three statements are true?
- f1 == f2
- f1 == f3
- f2 == f1[1]
- x == f1[0]
- f == f1[0]
import java.awt.Button; class CompareReference { public static void main(String [] args) { float f = 42.0f; float [] f1 = new float[2]; float [] f2 = new float[2]; float [] f3 = f1; long x = 42; f1[0] = 42.0f; } }
Options- A. 1, 2 and 3
- B. 2, 4 and 5
- C. 3, 4 and 5
- D. 1, 4 and 5 Discuss
Correct Answer: 2, 4 and 5
Explanation:
(2) is correct because the reference variables f1 and f3 refer to the same array object.(4) is correct because it is legal to compare integer and floating-point types.
(5) is correct because it is legal to compare a variable with an array element.
(3) is incorrect because f2 is an array object and f1[1] is an array element.
- 9. Which two of the following statements, inserted independently, could legally be inserted into missing section of this code?
- boolean test = (Component instanceof t);
- boolean test = (t instanceof Ticker);
- boolean test = t.instanceof(Ticker);
- boolean test = (t instanceof Component);
import java.awt.*; class Ticker extends Component { public static void main (String [] args) { Ticker t = new Ticker(); /* Missing Statements? */ } }
Options- A. 1 and 4
- B. 2 and 3
- C. 1 and 3
- D. 2 and 4 Discuss
Correct Answer: 2 and 4
Explanation:
(2) is correct because class type Ticker is part of the class hierarchy of t; therefore it is a legal use of the instanceof operator. (4) is also correct because Component is part of the hierarchy of t, because Ticker extends Component.(1) is incorrect because the syntax is wrong. A variable (or null) always appears before the instanceof operator, and a type appears after it. (3) is incorrect because the statement is used as a method (t.instanceof(Ticker);), which is illegal.
- 10. Which two statements are equivalent?
- 16*4
- 16>>2
- 16/2^2
- 16>>>2
Options- A. 1 and 2
- B. 2 and 4
- C. 3 and 4
- D. 1 and 3 Discuss
Correct Answer: 2 and 4
Explanation:
(2) is correct. 16 >> 2 = 4(4) is correct. 16 >>> 2 = 4
(1) is wrong. 16 * 4 = 64
(3) is wrong. 16/2 ^ 2 = 10
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- 1. What will be the output of the program?