Java - Core Java Exercises (3)

CORE JAVA – EXERCISES - 2 1.

What is the major mistake in the following code:

public class TryBlockDemo { public static void main( String[] args ) { divide( 15, 5 ); } private static void divide( int aDividend, int aDivisor ) { int mQuotient = 0; try { mQuotient = aDividend / aDivisor; } System.out.println( "The Quotient is: " + mQuotient ); } }

2.

What is the major mistake in the following code:

public class TryCatchBlockDemo { public static void main( String[] args ) { perform( "Hello", "World" ); } private static void perform( String aFirstString, String aSecondString ) { try { aFirstString = aFirstString + " " + aSecondString.substring( 1, 3 ); aFirstString = aFirstString + " "; } aFirstString = aFirstString + "Bye"; catch( Exception aWorkException ) { aWorkException.printStackTrace( return; }

);

System.out.println( "The Final String is: " + aFirstString ); return; } }

3.

Consider the following code:

import java.io.*; class ExceptionCatchingDemo2 { public static void main( String[] args ) { fileOperations( ); } private static void fileOperations( ) { try { ……… ……… throw new FileNotFoundException( ); ……… ……… } catch( FileNotFoundException aWorkFileNotFoundException ) { System.out.println( "File not found exception caught" ); aWorkFileNotFoundException.printStackTrace( ); } catch( IOException aWorkIOException ) { System.out.println( "IO exception caught" ); aWorkIOException.printStackTrace( ); } catch( ArrayIndexOutOfBoundsException aWorkArrayIndexOutOfBoundsException ) { System.out.println( "Array Index out of bounds exception caught" ); aWorkArrayIndexOutOfBoundsException.printStackTrace( ); } System.out.println( "File Operation completed" ); System.out.println( "Returning to caller ... " ); return; } }

i) ii)

Which of the catch blocks above will catch the thrown exception? Where will the execution proceed from, after that catch block has executed?

4.

Consider the following code:

import java.io.*; class ExceptionCatchingDemo { public static void main( String[] args ) { fileOperations( ); } private static void fileOperations( ) { try { ……… ……… throw new IOException( ); ……… ……… } catch( ArrayIndexOutOfBoundsException aWorkArrayIndexOutOfBoundsException ) { aWorkArrayIndexOutOfBoundsException.printStackTrace( ); } catch( Exception aWorkException ) { aWorkException.printStackTrace( ); } } }

Will the exception that is being thrown above get caught in any of the catch blocks? If so, which one and why? 5.

Consider the following code:

import java.io.*; class ExceptionCatchingDemo3 { public static void main( String[] args ) { fileOperations( ); } private static void fileOperations( ) { try { ……… ……… throw new IOException( );

……… ……… } catch( ArrayIndexOutOfBoundsException aWorkArrayIndexOutOfBoundsException ) { System.out.println( "Array Index out of bounds exception caught" ); aWorkArrayIndexOutOfBoundsException.printStackTrace( ); } catch( Exception aWorkException ) { System.out.println( "All exceptions caught" ); aWorkException.printStackTrace( ); } catch( IOException aWorkIOException ) { System.out.println( "IO exception caught" ); aWorkIOException.printStackTrace( ); } System.out.println( "File Operation completed" ); System.out.println( "Returning to caller ... " ); return; } }

What is the major error in the code above and why? Is it a run-time error? What is to be done to rectify the error?

6.

Consider the code below:

import java.io.*; class ExceptionPropagationDemo { public static void main( String[] args ) { try { System.out.println( "Entered main ... " ); ……… m1( ); ……… ……… } catch( Exception aWorkException ) { System.out.println( "Caught Exception in main" ); aWorkException.printStackTrace( ); } } private static void m1( ) { try { System.out.println( "Entered m1 ... " ); ……… ……… m2( ); ……… } catch( IOException aWorkIOException ) { System.out.println( "Caught IO Exception in m1" ); aWorkIOException.printStackTrace( ); } } private static void m2( ) throws IOException { // This method contains no try-catch block System.out.println( "Entered m2 ... " ); ……… ……… ……… } }

//

method code

Assume that a NullPointerException occurs in the method m2( ). i)

Describe with reasons how the exception would propagate up the method call sequence, and which catch block (if any) would finally catch it.

ii)

If we remove the try-catch structure from the main( ) function, what would happen to the exception?

7. Find the main mistake in the following code. Also suggest two possible ways to rectify it. import java.io.*; class ExceptionCatchingDemo4 { public static void main( String[] args ) { try { ……… fileOperations( ); ……… ……… } catch( Exception aWorkException ) { System.out.println( "Caught Exception in main" ); aWorkException.printStackTrace( ); } } private static void fileOperations( ) { // This method contains no try-catch block ……… ……… throw new IOException( ); ……… ……… } }

In Questions 1-4 below, choose the most appropriate answer: 8.

In order to read individual text characters from a text file, we use: i) ii) iii) iv)

9.

To write primitive Java data types to a binary file, we should use: i) ii) iii) iv)

10.

Writer FileWriter FileOutputStream OutputStreamWriter

To read primitive Java data types from a binary file, we should use: i) ii) iii) iv)

12.

FileOutputStream FileOutputStream wrapped over a DataOutputStream DataOutputStream DataOutputStream wrapped over a FileOutputStream

To write individual text characters to a text file, we use: i) ii) iii) ii)

11.

DataInputStream FileInputStream FileReader InputStreamReader

FileInputStream wrapped over a DataInputStream DataInputStream DataInputStream wrapped over a FileInputStream FileInputStream

Consider the following class:

class Entity { private int[] oEntityId = null; // other field declarations ……… public void setEntityId( int aEntityId, int aEntityIndex ) { oEntityId[aEntityIndex] = aEntityId; } // other method declarations ……… }

This class models a table called “ENTITY” in the database of the system. We want to use an object of this class to cache the data of the ENTITY table in memory temporarily, so that the front-end can access the data from the memory. However, in case of huge

amounts of data in this object, the application server will want to automatically save the object to a disk file temporarily, in order to avoid memory overflow. Can the application server save objects of the Entity class to disk? If not, what change is to be made in the class definition above?