Constructors And Methods — Part 1 MCQs with Explanations

Constructors are special methods in Java used to create objects of a class. They have the same name as the class itself. Unlike other methods, constructors don't have an explicit return type. Their job is to initialize the object's member variables (fields) with values. Therefore, they implicitly return a reference to the newly created object. The correct answer is option C, because it correctly states the return type is implicitly the same as the class name .

Only public, protected, private and default (no access modifier) are legal while declaring constructors.

a constructor call (super() or this() ) must be the first statement inside a constructor. No constructor calls are allowed inside a method. static void Tester() is a method not a constructor.

The correct answer is Option C: (int)(Math.random() + 0.5) In Java, to generate a random integer that can be either 0 or 1, you can use the `Math.random()` method, which returns a random double value between 0.0 (inclusive) and 1.0 (exclusive). To convert this into either 0 or 1, you need to add 0.5 to the result and then cast it to an integer using `(int)`. Here's the breakdown of the options: - Option A: `(int)Math.random()` would generate either 0 or a random positive integer, but not necessarily 1. - Option B: `(int)Math.random() + 1` would generate random positive integers starting from 1 and not 0. - Option C: `(int)(Math.random() + 0.5)` adds 0.5 to the random value, making it either 0.5 or 1.5, and then casts it to an integer, resulting in either 0 or 1, which is what you want. - Option D: `(int)(Math.random() + 0.2)` would not reliably generate only 0 or 1; it can produce a range of integers starting from 0.

The method floor gives the largest integer that is less than or equal to the argument.

Only public, protected, private and default(no modifier) are legal when declaring constructors.

super() call must be the first statement in a constructor.

random() is a static method defined in Math class. Syntax: static double random() random() always return a value in the range 0.0 <= Math.random() <1.0 So, taking floor function of any number between above range always yield 0.0. Ex: Math.floor(0.958127101241...) = 0.0 Math.floor(0.05684865565...) = 0.0

The given program creates a class Num that has a constructor with a double parameter. In the main method, an object of the Num class is created with the value 2, which is passed as a double value. Since 2 is treated as an integer, Java automatically converts it to a double (2.0), and the constructor prints this value. Thus, the output of the program is 2.0.

Overloading depends only on the method or constructor name and its parameter list i.e. method(int i) and method(String str) So, overloading does not depend on access modifiers(public, private, protected), access specifiers(static, final) and return type.

Return type of method display is int and we are trying to return string.

Constructors are special methods in Java used to create objects of a class. Unlike other methods, constructors don't have an explicit return type. They don't use keywords like void , int , etc. to specify what they return. Instead, their job is to initialize the object being created, setting initial values for its member variables. When a constructor is called, it automatically returns a newly created object of the class. Therefore, the implicit return type of a constructor is the class object itself. So the correct option is B .

Option A and B are wrong because they use the default access modifier and the access modifier for the class is public (remember, the default constructor has the same access modifier as the class). Option C is wrong. The void makes the compiler think that this is a method specification - in fact if it were a method specification the compiler would spit it out.

The code will result in a compilation error because in the method myMethod, the use of this() is incorrect. In Java, this() is used to call another constructor, but it can only be used in a constructor, not in a method. Using this() in myMethod causes a compilation error. Thus, the program will not compile, and the correct answer is a Compilation Error.

Step-by-step breakdown: 1. The main method in the Test class creates an instance of MyClass called obj. 2. The val field of obj is set to 1 with obj.val = 1. 3. The call method is invoked on obj with obj itself as the argument: obj.call(obj). 4. Inside the call method, the val field of the passed MyClass instance (ref) is incremented by 1 using ref.val++. Since ref refers to obj, this increments obj.val from 1 to 2. 5. Finally, System.out.println(obj.val) prints the value of obj.val, which is now 2. Therefore, the output of the program is 2 .

Choice A,C are the correct answers. The default access specifier for any constructor is same as the access specifier of class.so the options A and C are correct.

Cannot make a static reference to the non-static method add(int, int) from the type A. The short s is autoboxed correctly, but the add() method cannot be invoked from a static method because add() method is not static.

Primitive widening uses the smallest method argument possible. (For Example if you pass short value to a method but method with short argument is not available then compiler chooses method with int argument). But in this case compiler will prefer the older style before it chooses the newer style, to keep existing code more robust. var-args method is looser than wider.

Constructor of class B call their superclass constructor of class A (public A()), which execute first, and that constructors can be overloaded. Then come to constructor of class B (public B (int i)).

Choice A is the correct answer. The code does not compile because the constructor of class A is declared as private. This creates a problem when the subclass constructor makes an implicit super() call to the parent class constructor at the time B is instantiated. Since the code does not compile, all the other choices are incorrect. If the constructor of A had not been private, the output would have been 7.

Let's break down why the answer is a Runtime Error . The problem lies within the `func` method of the `recursion` class. It's trying to use recursion , which means a function calling itself. Here's the critical issue: The `func` method calls itself (`func(n - 1)`) without a base case . A base case is a condition that stops the recursive calls. Without a base case, the function keeps calling itself again and again. Imagine `func(12)` is called. It then calls `func(11)`, then `func(10)`, and so on. This continues indefinitely, each call placing another "frame" onto the call stack (memory used to track function calls). Eventually, the call stack runs out of space. This is called a StackOverflowError . StackOverflowError is a type of Runtime Error . Because the error happens while the program is running (not during compilation), it's a runtime error. Therefore, the correct answer is Option D: Runtime Error .

A special method to create instances of classes is the correct answer to “What is a constructor in Java”. This question is standard in competitive examination syllabi for Constructors And Methods.

public is the correct answer to “Which keyword is used to define a method in Java”. This question is standard in competitive examination syllabi for Constructors And Methods.

constructor() is the correct answer to “In Java, which method is automatically called when an object is created”. This question is standard in competitive examination syllabi for Constructors And Methods.

Defining multiple methods with the same name in the same class is the correct answer to “What is method overloading in Java”. This question is standard in competitive examination syllabi for Constructors And Methods.

The method does not return any value is the correct answer to “What does the "void" keyword indicate in a method declaration”. This question is standard in competitive examination syllabi for Constructors And Methods.

package-private (no modifier) is the correct answer to “Which access modifier is used for a method that can be accessed from any class in the same package”. This question is standard in competitive examination syllabi for Constructors And Methods.

To refer to the current instance of the class is the correct answer to “What is the purpose of the "this" keyword in Java constructors and methods”. This question is standard in competitive examination syllabi for Constructors And Methods.

final is the correct answer to “Which keyword is used to prevent method overriding in Java”. This question is standard in competitive examination syllabi for Constructors And Methods.

myObject.myMethod() is the correct answer to “What is the correct syntax to call a method named "myMethod" from an object "myObject"”. This question is standard in competitive examination syllabi for Constructors And Methods.

finalize() is the correct answer to “Which method is called when an object is garbage collected in Java”. This question is standard in competitive examination syllabi for Constructors And Methods.

No, constructors do not have a return type is the correct answer to “In Java, can a constructor have a return type”. This question is standard in competitive examination syllabi for Constructors And Methods.

Defining a new method with the same name in a subclass is the correct answer to “What is method overriding in Java”. This question is standard in competitive examination syllabi for Constructors And Methods.

To call the superclass constructor is the correct answer to “In Java, what is the purpose of the "super" keyword in a constructor”. This question is standard in competitive examination syllabi for Constructors And Methods.

A method that belongs to the class rather than an instance is the correct answer to “What is a "static" method in Java”. This question is standard in competitive examination syllabi for Constructors And Methods.

A constructor with parameters that initialize object properties is the correct answer to “What is a parameterized constructor in Java”. This question is standard in competitive examination syllabi for Constructors And Methods.

super is the correct answer to “Which keyword is used to call the constructor of the superclass in a subclass constructor”. This question is standard in competitive examination syllabi for Constructors And Methods.

To pass values into a method is the correct answer to “What is the purpose of method parameters in Java”. This question is standard in competitive examination syllabi for Constructors And Methods.

abstract is the correct answer to “In Java, which keyword is used to define an abstract method”. This question is standard in competitive examination syllabi for Constructors And Methods.

Calling multiple methods on the same object in a single line is the correct answer to “What is method chaining in Java”. This question is standard in competitive examination syllabi for Constructors And Methods.