Correct Answers :

[A, C]

Explanation :

The Java Virtual Machine calls and executes the main method.

Correct Answers :

[C]

Explanation :

If the variable courseName is defined as a private member, it won’t be accessible from the class EJavaGuru. An attempt to do so will cause it to fail at compile time. Because the code won’t compile, it can’t execute.

Correct Answers :

[C]

Explanation :

The class will fail to compile because a non-public class cannot be accessed outside a package in which it is defined. The class Course therefore can't be accessed from within the class EJavaGuru, even if it is explicitly imported into it. If the class itself isn’t accessible, there’s no point in accessing a public member of a class.

Correct Answers :

[A, D]

Explanation :

Options (a) and (d) are correct. Use a long data type to store big number values, a boolean data type to store yes/no values as true/false, and a double or float to store decimal numbers.
Option (b) is incorrect. You can’t use an int to store yes/no or true/false values.
Option (c) is incorrect. You can’t use a char data type to store very long values. Also, it's conceptually incorrect to track counts using the char data type.

Correct Answers :

[C, D, F, G]

Explanation :

Options (a) and (b) are incorrect. There are no primitive data types in Java with the names bit and integer. The correct names are byte and int.
Option (c) is correct. It assigns a hexadecimal literal value to the variable a3.
Option (d) is correct. It assigns an octal literal value to the variable a4.
Option (e) is incorrect. It defines a variable of type double, which is used to store decimal numbers, not integers.
Option (f) is correct. -0 is a valid literal value.
Option (g) is correct. 123456789 is a valid integer literal value that can be assigned to a variable of type long.

Correct Answers :

[A, C]

Explanation :

To output a value of 11, the value of the variable ctr should be 51 because 51%20 is 11. Operator % outputs the remainder from a division operation.
The current value of the variable ctr is 50. It can be incremented by 1 using the correct assignment or increment operator.
Option (b) is incorrect. Java does not define a =+ operator. The correct operator is +=.
Option (d) is incorrect because it’s assigning a value of 1 to the variable result, not incrementing it by 1.

Correct Answers :

[C, D, E, F, G]

Explanation :

Option (a) is incorrect. Overloaded methods can change the access modifiers, but changing the access modifier alone won’t make it an overloaded method. This option also changes the names of the method parameters, but that doesn’t make any difference to a method signature.

Option (b) is incorrect. Overloaded methods can change the return type of the method, but changing the return type won’t make it an overloaded method. Option (c) is correct. Changing the placement of the types of the method parameters overloads it.

Option (d) is correct. Changing the return type of a method and the placement of the types of the method parameters overloads it. Option (e) is correct. Changing the return type of a method and making a change in the parameter list overload it.

Option (f) is correct. Changing the return type of a method and making a change in the parameter list overload it.
Option (g) is correct. Changing the parameter list also overloads a method.

Correct Answers :

[C]

Explanation :

No compilation issues exist with the code. You can overload methods by changing the type of the method arguments in the list. Using method arguments with data types having a base-derived class relationship (Object and String classes) is acceptable. Using method arguments with data types for which one can be automatically converted to the other (int and long) is also acceptable.

When the code executes course.enroll(c), char can be passed to two overloaded enroll methods that accept int and long.

The char gets expanded to its nearest type—int—so course.enroll(c) calls the overloaded method that accepts int, printing int. The code course.enroll("Object") is passed a String value. Although String is also an Object, this method calls the specific (not general) type of the argument passed to it. So course.enroll("Object") calls the overloaded method that accepts String, printing String.

Correct Answers :

[A, D]

Explanation :

You can define overloaded constructors with different access modifiers in the same way that you define overloaded methods with different access modifiers. But a change in only the access modifier can’t be used to define overloaded methods or constructors. private methods and constructors are also counted as overloaded methods.

The following line of code calls EJava’s constructor, which doesn't accept any method argument:

EJava eJava = new EJava();

The no-argument constructor of this class calls the constructor that accepts an int argument, which in turn calls the constructor with the String argument. Because the constructor with the String constructor doesn't call any other methods, it prints protected and returns control to the constructor that accepts an int argument. This constructor prints private and returns control back to the constructor that doesn't accept any method argument. This constructor prints public and returns control to the main method.

Correct Answers :

[D, E]

Explanation :

Option (a) is incorrect. By default, an ArrayList creates an array with an initial size of 10 to store its elements.
Option (b) is incorrect. Starting with Java 7, switch also accepts variables of type String. Because a String can be stored in an ArrayList, you can use elements of an ArrayList in a switch construct.

Option (c) is incorrect. Only remove() will remove all elements of an ArrayList. Option (d) is correct. An ArrayList internally uses an array to store all its elements.

Whenever you add an element to an ArrayList, it checks whether the array can accommodate the new value. If it can’t, ArrayList creates a larger array, copies all the existing values to the new array, and then adds the new value at the end of the array. If you frequently add elements to an ArrayList, it makes sense to create an ArrayList with a bigger capacity because the previous process isn’t repeated for each ArrayList insertion.

Option (e) is correct. Calling clone() on an ArrayList will create a separate reference variable that stores the same number of elements as the ArrayList to be cloned. But each individual ArrayList element will refer to the same object; that is, the individual ArrayList elements aren’t cloned.

Correct Answers :

[A, B, C, E]

Explanation :

Option (a) is correct. A developer may prefer using an ArrayList over an array because it offers all the benefits of an array and a list. For example, you can easily add or remove elements from an ArrayList.

Option (b) is correct.

Option (c) is correct. An ArrayList can be easily searched, sorted, and have its values compared using the methods provided by the Collection framework classes.

Option (d) is incorrect. An array requires you to specify the total number of elements before you can add any element to it. But you don’t need to specify the total number of elements that you may add to an ArrayList at any time in your code.

Option (e) is correct.

Correct Answers :

[A, D, E, H, J]

Explanation :

Line 7: The method contains accepts an object and compares it with the values stored in the list. It returns true if the method finds a match and false otherwise. This method uses the equals method defined by the object stored in the list. In the example, the ArrayList stores objects of class String, which has overridden the equals method. The equals method of the String class compares the values stored by it. This is why line 7 returns the value true.

Line 8: indexOf returns the index position of an element if a match is found; otherwise, it returns -1. This method also uses the equals method behind the scenes to compare the values in an ArrayList. Because the equals method in class String compares its values and not the reference variables, the indexOf method finds a match in position 1.

Line 9: The clear method removes all the individual elements of an ArrayList such that an attempt to access any of the earlier ArrayList elements will throw a runtime exception. It doesn’t set the ArrayList reference variable to null.

Line 10: ArrayList has overridden the toString method such that it returns a list of all its elements enclosed within square brackets. To print each element, the toString method is called to retrieve its String representation.

Line 11: The clear method removes all the elements of an ArrayList. An attempt to access the (nonexistent) ArrayList element throws a runtime IndexOutOfBounds- Exception exception.

This question tests your understanding of ArrayList and determining the equality of String objects.

Correct Answers :

[A]

Explanation :

For a switch case construct, control enters the case labels when a matching case is found. The control then falls through the remaining case labels until it's terminated by a break statement. The control exits the switch construct when it encounters a break statement or it reaches the end of the switch construct.

In this question, a matching label is found for case label 120. The control executes the statement for this case label and prints ejava to the console. Because a break statement doesn’t terminate the case label, the control falls through to case label 121.

The control executes the statement for this case label and prints enum to the console.

Because a break statement also doesn’t terminate this case label, the control falls through to case label 127. The control executes the statement for this case label and prints guru to the console. This case label is terminated by a break statement, so the control exits the switch construct.

Correct Answers :

[C]

Explanation :

The expression used in the if construct isn't comparing the value of the variable myVal with the literal value true—it's assigning the literal value true to it. The assignment operator (=) assigns the literal value. The comparison operator (==) is used to compare values.

Because the resulting value is a boolean value, the compiler doesn't complain about the assignment in the if construct.

The for loop is part of the if construct, which prints 0 and 1. The else part doesn’t execute because the if condition evaluates to true. The code has no compilation errors.

Correct Answers :

[F]

Explanation :

First of all, the following line of code has no compilation errors:
for (; i < 2; i=i+5) {
Using the initialization block is optional in a for loop. In this case, using a semicolon (;) terminates it.

For the first for iteration, the variable i has a value of 0. Because this value is less than 2, the following if construct evaluates to true and the continue statement executes:

if (i < 5) continue;

Because the continue statement ignores all of the remaining statements in a for loop iteration, the control doesn’t print the value of the variable i, which leads the control to move on to the next for iteration. In the next for iteration, the value of the variable i is 5. The for loop condition evaluates to false and the control moves out of the for loop. After the for loop, the code prints out the value of the variable i, which increments once using the code i=i+5.

Correct Answers :

[A, B]

Explanation :

Option (a) is correct. Inheritance can allow you to reuse existing code by extending a class. In this way, the functionality that is already defined in the base class need not be defined in the derived class. The functionality offered by the base class can be accessed in the derived class as if it were defined in the derived class.

Option (b) is correct. Common code can be placed in the base class, which can be extended by all the derived classes. If any changes need to be made to this common code, it can be modified in the base class. The modified code will be accessible to all the derived classes.

Option (c) is incorrect. Polymorphism doesn’t pass any special instructions to the compiler to make the Java code execute on multiple platforms. Java code can execute on multiple platforms because the Java compiler compiles to virtual machine code, which is platform-neutral. Different platforms implement this virtual machine.

Option (d) is incorrect. Polymorphic methods can throw exceptions.

Correct Answers :

[A]

Explanation :

All of these options define classes. When methods with the same method signature are defined in classes that share an inheritance relationship, the methods are considered polymorphic.

Correct Answers :

[D]

Explanation :

The given code does not define any method in the class Person that is redefined or implemented in the classes Employee and Doctor. Though the classes Employee and Doctor extend the class Person, all these three polymorphism concepts or design principles are based on a method, which is missing in these classes.

Correct Answers :

[C, D]

Explanation :

Option (a) is a true statement. A checked exception is a subclass of java.lang .Exception, and a runtime exception is a subclass of java.lang.RuntimeException.
java.lang.RuntimeException is a subclass of java.lang.Exception, and java.lang .Exception is a subclass of java.lang.Throwable. Hence, all the exceptions are subclasses of java.lang.Throwable.

Option (b) is also a true statement. Unchecked exceptions are subclasses of class java.lang.RuntimeException, which itself is a subclass of java.lang.Exception. Hence, a class can be a subclass of class java.lang.Exception and either a checked or an unchecked exception.

Option (c) is a false statement. Error is not an exception. It does not subclass java.lang.Exception.

Option (d) is also a false statement. Error need not be part of a method signature, but checked exceptions must be a part of the method signatures.

Correct Answers :

[C]

Explanation :

The try block executes, incrementing the value of variable a to 11. This step is followed by execution of the finally block, which also increments the value of variable a by 1, to 12. The method tryAgain returns the value 12, which is printed by the method main.

There are no compilation issues with the code. A try block can be followed by a finally block, without any catch blocks. Even though the try block doesn’t throw any exceptions, it compiles successfully. The following is an example of a try-catch block that won’t compile because it tries to catch a checked exception that's never thrown by the try block:

try {
++a;
}
catch (java.io.FileNotFoundException e) {
}