Java Constructors and Methods Overview
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What is the purpose of the 'this' keyword in the context of constructor calls?

  • To return the current instance of the class
  • To refer to global variables of the class
  • To create a new instance of a class
  • To pass the current object as a parameter to another constructor (correct)

    • In the provided code, what will be the output when s1.display() is called?

  • Error due to missing fee parameter
  • 111 ankit java 6000.0
  • 111 ankit java 0.0 (correct)
  • 112 sumit java 6000.0

    • What happens if the this keyword is not used in the constructor call?

  • The object will not be initialized
  • Compilation error occurs (correct)
  • The class will not compile at all
  • The constructor will not have access to class variables

    • What will the m method in the S2 class print when called from the p method?

    <p>method is invoked</p> Signup and view all the answers

    Which of the following statements about the 'this' keyword is true?

    <p>It allows passing the current object to methods and constructors</p> Signup and view all the answers

    What is the main purpose of a constructor in Java?

    <p>To initialize the state of an object</p> Signup and view all the answers

    Which of the following statements about methods in Java is true?

    <p>A method can return a value.</p> Signup and view all the answers

    What distinguishes a constructor from a method in Java?

    <p>Constructors do not have a return type, while methods do.</p> Signup and view all the answers

    How can the values of one object be copied to another in Java?

    <p>By using a constructor, assigning values, or clone() method</p> Signup and view all the answers

    What is the requirement for the name of a constructor in Java?

    <p>It must be the same as the class name.</p> Signup and view all the answers

    Which of the following is NOT a way to refer to the current object in Java?

    <p>current</p> Signup and view all the answers

    What happens if no constructor is explicitly defined in a class?

    <p>The Java compiler provides a default constructor.</p> Signup and view all the answers

    Which statement is true regarding the use of 'this' keyword in Java?

    <p>It can be used to refer to the current class instance variable.</p> Signup and view all the answers

    What is the purpose of using the 'this' keyword in Java?

    <p>To refer to the current class instance variable</p> Signup and view all the answers

    How can 'this' be used to resolve ambiguity in constructor parameters?

    <p>By using 'this' to refer to instance variables</p> Signup and view all the answers

    Which statement about invoking methods using 'this' is true?

    <p>The compiler automatically adds 'this' if not used</p> Signup and view all the answers

    When using 'this()' in a constructor, what is the effect of this call?

    <p>It can invoke another constructor from the same class</p> Signup and view all the answers

    What happens if 'this' is omitted in method calls within the same class?

    <p>The call is treated as if 'this' was included</p> Signup and view all the answers

    In the given example, how is 'this' used in the Student class constructor?

    <p>To initialize instance variables with parameter values</p> Signup and view all the answers

    What is the best practice regarding variable naming when using 'this' in Java?

    <p>Use meaningful names for variables</p> Signup and view all the answers

    Which statement correctly describes 'this' in relation to method calls?

    <p>'this' will not work if the method is static</p> Signup and view all the answers

    Which purpose does the 'this' keyword serve in a method?

    <p>It refers to the current instance of the class.</p> Signup and view all the answers

    In the example provided, what is the output of the 'display' method in class B?

    <p>10, because it prints the data member of A4.</p> Signup and view all the answers

    What will be printed when the 'm' method in class A5 is executed?

    <p>The reference ID of A5 object.</p> Signup and view all the answers

    What does the finalize() method belong to?

    <p>The Object class.</p> Signup and view all the answers

    What is a necessary condition for a method to return 'this'?

    <p>The return type must match the class type.</p> Signup and view all the answers

    What happens when you run the main method in class Test1?

    <p>It creates an instance of class A and prints 'Hello Java'.</p> Signup and view all the answers

    Which statement about the finalize() method is correct?

    <p>It is called by the Garbage Collector for cleanup.</p> Signup and view all the answers

    Which of the following correctly initializes an instance of class A and invokes the display function?

    <p>new A().getA();</p> Signup and view all the answers

    What will be the output of the display method for the object s1 after calling Student.change()?

    <p>111 Karan BBDIT</p> Signup and view all the answers

    Which of the following statements is true regarding static methods in Java?

    <p>Only one copy of a static method exists irrespective of object instantiation.</p> Signup and view all the answers

    What is the result of calling Calculate.cube(5)?

    <p>125</p> Signup and view all the answers

    Which restriction is NOT applicable to a static method in Java?

    <p>Static methods must be public.</p> Signup and view all the answers

    What will be printed when the main method of the TestStaticMethod class runs?

    <p>111 Karan BBDIT 222 Aryan BBDIT 333 Sonoo BBDIT</p> Signup and view all the answers

    What will happen if you try to access a non-static method inside a static method?

    <p>It will throw a compile-time error.</p> Signup and view all the answers

    How can you change the static variable college to a different value?

    <p>By calling the change() method of the Student class.</p> Signup and view all the answers

    In the Student class, which method is used to create an instance?

    <p>constructor</p> Signup and view all the answers

    Study Notes

    Java Constructor

    • Definition: A constructor initializes the state of an object.
    • Characteristics:
      • It does not have a return type.
      • It is invoked implicitly.
      • The compiler provides a default constructor if none is defined.
      • The constructor name must match the class name.

    Java Method

    • Definition: A method exposes the behavior of an object.
    • Characteristics:
      • It must have a return type.
      • It is invoked explicitly.
      • The method name can be different from the class name.

    Java Copy Constructor

    • There is no direct copy constructor in Java as in C++.
    • To copy values from one object to another, use methods like:
      • Constructor: Pass an object as an argument.
      • Assigning values: Assign each attribute of the object individually.
      • clone() method: Creates a shallow copy of the object using Object class's clone() method.

    'this' Keyword Usage

    • Definition: The this keyword refers to the current object within a class.
    • Uses:
      • Refer to class instance variables: Used to resolve ambiguity between instance variables and local variables with the same name.
      • Invoke current class method: Implicitly included when calling a method within the same class.
      • Invoke current class constructor: Used for constructor chaining (this()) to invoke another constructor within the same class.
      • Pass as argument: Used to pass the current object as an argument to a method or constructor.
      • Return current class instance: Return the current object from a method.

    Static Methods

    • Definition: Methods defined as static belong to a class, not an object.
    • Characteristics:
      • They are accessed using the class name, not an object instance.
      • They operate on class-level variables or data.
      • They cannot directly access non-static members (variables or methods) of the class.

    finalize() Method

    • Definition: A method of the Object class, available to all Java classes.
    • Characteristics:
      • It is a non-static and protected method.
      • Invoked by the garbage collector to clean up resources before an object is garbage collected.

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    Description

    This quiz covers the fundamentals of Java constructors and methods, including their definitions, characteristics, and differences. You will also learn about the 'this' keyword and copy mechanisms in Java. Test your knowledge to enhance your understanding of object-oriented programming in Java.

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