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Home Java Programming Assertions See What Others Are Saying!
  • Question
  • Which statement is true about assertions in the Java programming language?


  • Options
  • A. Assertion expressions should not contain side effects.
  • B. Assertion expression values can be any primitive type.
  • C. Assertions should be used for enforcing preconditions on public methods.
  • D. An AssertionError thrown as a result of a failed assertion should always be handled by the enclosing method.

  • Correct Answer
  • Assertion expressions should not contain side effects. 

    Explanation
    Option A is correct. Because assertions may be disabled, programs must not assume that the boolean expressions contained in assertions will be evaluated. Thus these expressions should be free of side effects. That is, evaluating such an expression should not affect any state that is visible after the evaluation is complete. Although it is not illegal for a boolean expression contained in an assertion to have a side effect, it is generally inappropriate, as it could cause program behaviour to vary depending on whether assertions are enabled or disabled.

    Assertion checking may be disabled for increased performance. Typically, assertion checking is enabled during program development and testing and disabled for deployment.

    Option B is wrong. Because you assert that something is "true". True is Boolean. So, an expression must evaluate to Boolean, not int or byte or anything else. Use the same rules for an assertion expression that you would use for a while condition.

    Option C is wrong. Usually, enforcing a precondition on a public method is done by condition-checking code that you write yourself, to give you specific exceptions.

    Option D is wrong. "You're never supposed to handle an assertion failure"

    Not all legal uses of assertions are considered appropriate. As with so much of Java, you can abuse the intended use for assertions, despite the best efforts of Sun's Java engineers to discourage you. For example, you're never supposed to handle an assertion failure. That means don't catch it with a catch clause and attempt to recover. Legally, however, AssertionError is a subclass of Throwable, so it can be caught. But just don't do it! If you're going to try to recover from something, it should be an exception. To discourage you from trying to substitute an assertion for an exception, the AssertionError doesn't provide access to the object that generated it. All you get is the String message.


    More questions

    • 1. Which is a reserved word in the Java programming language?

    • Options
    • A. method
    • B. native
    • C. subclasses
    • D. reference
    • E. array
    • Discuss
    • 2. Which statement is true for the class java.util.ArrayList?

    • Options
    • A. The elements in the collection are ordered.
    • B. The collection is guaranteed to be immutable.
    • C. The elements in the collection are guaranteed to be unique.
    • D. The elements in the collection are accessed using a unique key.
    • Discuss
    • 3. What will be the output of the program?
      public class Test 
      { 
          public static void main(String[] args) 
          {
              final StringBuffer a = new StringBuffer(); 
              final StringBuffer b = new StringBuffer(); 
      
              new Thread() 
              { 
                  public void run() 
                  {
                      System.out.print(a.append("A")); 
                      synchronized(b) 
                      { 
                          System.out.print(b.append("B")); 
                      } 
                  } 
              }.start(); 
                  
              new Thread() 
              {
                  public void run() 
                  {
                      System.out.print(b.append("C")); 
                      synchronized(a) 
                      {
                          System.out.print(a.append("D")); 
                      } 
                  } 
              }.start(); 
          } 
      }
      

    • Options
    • A. ACCBAD
    • B. ABBCAD
    • C. CDDACB
    • D. Indeterminate output
    • Discuss
    • 4. Which is true about a method-local inner class?

    • Options
    • A. It must be marked final.
    • B. It can be marked abstract.
    • C. It can be marked public.
    • D. It can be marked static.
    • Discuss
    • 5. Given that all methods of class FileOutputStream, including close(), throw an IOException, which of these is true?
      import java.io.*;
      public class MyProgram 
      {
          public static void main(String args[])
          {
              FileOutputStream out = null;
              try 
              {
                  out = new FileOutputStream("test.txt");
                  out.write(122);
              }
              catch(IOException io) 
              {
                  System.out.println("IO Error.");
              }
              finally 
              {
                  out.close();
              }
          }
      }
      

    • Options
    • A. This program will compile successfully.
    • B. This program fails to compile due to an error at line 4.
    • C. This program fails to compile due to an error at line 6.
    • D. This program fails to compile due to an error at line 18.
    • Discuss
    • 6. What will be the output of the program?
      public class Test 
      {
          public static void main(String [] args) 
          {
              int I = 1;
              do while ( I < 1 )
              System.out.print("I is " + I);
              while ( I > 1 ) ;
          }
      }
      

    • Options
    • A. I is 1
    • B. I is 1 I is 1
    • C. No output is produced.
    • D. Compilation error
    • Discuss
    • 7. What will be the output of the program?
      class MyThread extends Thread 
      {
          public static void main(String [] args) 
          {
              MyThread t = new MyThread();
              Thread x = new Thread(t);
              x.start(); /* Line 7 */
          }
          public void run() 
          {
              for(int i = 0; i < 3; ++i) 
              {
                  System.out.print(i + "..");
              }
          }
      }
      

    • Options
    • A. Compilation fails.
    • B. 1..2..3..
    • C. 0..1..2..3..
    • D. 0..1..2..
    • Discuss
    • 8. Which of the following is/are legal method declarations?

      1. protected abstract void m1();
      2. static final void m1(){}
      3. synchronized public final void m1() {}
      4. private native void m1();

    • Options
    • A. 1 and 3
    • B. 2 and 4
    • C. 1 only
    • D. All of them are legal declarations.
    • Discuss
    • 9. Which three statements are true?
      1. f1 == f2
      2. f1 == f3
      3. f2 == f1[1]
      4. x == f1[0]
      5. 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
    • 10. Which one create an anonymous inner class from within class Bar?
      class Boo 
      {
          Boo(String s) { }
          Boo() { }
      }
      class Bar extends Boo 
      {
          Bar() { }
          Bar(String s) {super(s);}
          void zoo() 
          {
          // insert code here
          }
      }
      

    • Options
    • A. Boo f = new Boo(24) { };
    • B. Boo f = new Bar() { };
    • C. Bar f = new Boo(String s) { };
    • D. Boo f = new Boo.Bar(String s) { };
    • Discuss


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