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String Operations in Java
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String Operations in Java

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Questions and Answers

What does the compareTo() method return when the first string is lexicographically greater than the second string?

  • An int > 0 (correct)
  • An int < 0
  • True
  • 0

    • When using the equals() method, what does a return value of false indicate?

  • One of the strings is null.
  • The two strings are not equal. (correct)
  • The two strings are equal.
  • The two strings have different lengths.

    • Which method should be used to determine the case-insensitive lexicographical order of two strings?

  • equalsIgnoreCase(String str)
  • equals(Object obj)
  • compareToIgnoreCase(String str) (correct)
  • compareTo(String str)

    • What is the primary purpose of the equals() method in string operations?

    <p>To check if two strings are identical.</p> Signup and view all the answers

    Which class must be imported to use the Scanner for console input in Java?

    <p>java.util.Scanner</p> Signup and view all the answers

    What is the primary purpose of a constructor in a class?

    <p>To create an object instance</p> Signup and view all the answers

    What does it mean to overload a constructor?

    <p>Having multiple constructors with the same name but different number or type of parameters</p> Signup and view all the answers

    What happens if you do not declare a constructor in a Java class?

    <p>Java automatically provides a default constructor</p> Signup and view all the answers

    How would you instantiate an object using a constructor that requires parameters?

    <p>Student s = new Student('Zina', '3003456');</p> Signup and view all the answers

    Which of the following statements about constructors is true?

    <p>Constructors with the same name must have different parameter lists.</p> Signup and view all the answers

    In order to create a dog object with specified fields, which line of code demonstrates the correct constructor call?

    <p>Dog d = new Dog('Buddy', 'Beagle', 20.5);</p> Signup and view all the answers

    Which of the following best describes a constructor with parameters?

    <p>It allows for custom initial values for fields.</p> Signup and view all the answers

    If a class has a user-defined constructor, what happens to the default constructor?

    <p>It is no longer available.</p> Signup and view all the answers

    What should be noted about String objects once they are instantiated?

    <p>They are final and cannot be changed.</p> Signup and view all the answers

    Which operation should be performed to display a welcome message using str3?

    <p>Display 'Welcome: ' followed by str3.</p> Signup and view all the answers

    What is the primary role of a mutator method in a class?

    <p>To set or modify the value of an instance variable</p> Signup and view all the answers

    What is the correct way to compare the values of Strings in Java?

    <p>Using the equals method.</p> Signup and view all the answers

    Which statement correctly describes accessor methods?

    <p>They return the value of a specific instance field.</p> Signup and view all the answers

    What should be the initial value of str3 in the StringOperations class?

    <p>It should not be initialized with a value.</p> Signup and view all the answers

    What is a common characteristic of functional methods in a class?

    <p>They perform some sort of function or behavior for the class.</p> Signup and view all the answers

    What is the result of displaying a substring of str3 from character 0 to character 5?

    <p>It will display 'You a'.</p> Signup and view all the answers

    What must be true about parameters when calling a method?

    <p>They must match the type specified in the method definition.</p> Signup and view all the answers

    Which of the following best describes a method signature?

    <p>The name of the method along with its parameters.</p> Signup and view all the answers

    How do mutator methods differ from accessor methods?

    <p>Mutator methods have void return types.</p> Signup and view all the answers

    What kind of method would likely include parameters as needed?

    <p>Functional method</p> Signup and view all the answers

    What identifies the return type of a method when it is invoked?

    <p>The return type declared in the method signature</p> Signup and view all the answers

    What does encapsulation in object-oriented programming primarily achieve?

    <p>Hides the internal workings of a class from the user</p> Signup and view all the answers

    Which statement about Java's inheritance model is true?

    <p>Java supports only single inheritance</p> Signup and view all the answers

    How can private data fields in a class be accessed?

    <p>Through public methods that provide controlled access</p> Signup and view all the answers

    What must be done to store fish objects in the system according to the new requirements?

    <p>A fish constructor must reflect all required values</p> Signup and view all the answers

    Which of the following describes a superclass in the context of the Animal class?

    <p>The parent class that contains common fields and methods</p> Signup and view all the answers

    What is the primary purpose of encapsulating data in object-oriented programming?

    <p>To ensure data can only be modified through designated methods</p> Signup and view all the answers

    When displaying values of both Fish and Dog classes, what should be done?

    <p>Display each class's values separately using their respective methods</p> Signup and view all the answers

    A fish can be classified as what types of varieties?

    <p>Either cold or heated water varieties</p> Signup and view all the answers

    Study Notes

    String Operations

    • String objects in Java are immutable once instantiated, meaning their values cannot be changed.
    • String class provides various methods for manipulation and operation on strings.

    StringVariables and Initialization

    • Create a class named StringOperations with three string variables: str1 (initialized to "Hello"), str2 (your first name), str3 (uninitialized).
    • Assign a concatenated value to str3, joining "You are " with str2.

    Output and Display

    • Display a welcome message with the content of str3.
    • Show a substring of str3 from index 0 to 5.
    • Output str2 in uppercase format.

    String Comparison Best Practices

    • Use == operator cautiously with strings; it compares references, not values.
    • For proper string comparison, use:
      • compareTo(String str) for lexicographical order.
      • equals(Object obj) for value comparison.

    CompareTo and Equals Methods

    • s1.compareTo(s2) returns:
      • A negative integer if s1 is lexically less than s2.
      • Zero if they are equal.
      • A positive integer if s1 is greater.
    • s1.equals(s2) returns a boolean indicating if both strings are equal.

    Lexicographical Comparison

    • Implement comparisons between str1 and str2. Display the lexicographical order if they are not equal.
    • Show which strings are the same or not, regardless of the order.

    User Input with Scanner

    • To read user input, import java.util.Scanner and initialize: Scanner sc = new Scanner(System.in);.

    Constructors

    • Constructors in Java create instances of classes using the new keyword.
    • A class can have multiple constructors (overloading), distinguished by argument types/quantity.
    • The default constructor is provided by Java if no constructor is declared.

    Example of Constructor Usage

    • To instantiate a Student: Student stu = new Student(); with parameters as needed.

    Object/Instance Fields

    • Instance fields for a dog class may include String name, String breed, String barkNoise, and double weight.

    Method Components

    • Method signatures include name, parameters, and return type (void if no return).
    • Accessor (getter) methods return values of specific fields, while mutator (setter) methods modify them.

    Functional Methods

    • Functional methods perform various operations, returning void or values as needed.

    Encapsulation

    • Encapsulation conceals the internal workings of an object, using private fields with public methods for access.
    • It protects data integrity by preventing unauthorized access or modification.

    Inheritance and Class Structure

    • Java supports single inheritance; subclass properties/methods extend those of the superclass.
    • Common fields/methods should reside in a superclass, while specific fields/methods belong in respective subclasses.

    Fish and Animal Classes

    • Introduce an Animal superclass and Fish subclass for managing various animal types in the application.
    • Each animal type must include specific attributes like color and constructor methods for initialization.

    Final Notes

    • Ensure all required values for fish objects are provided before instantiation.
    • Implement logic to display details for both fish and dog objects, highlighting their differences and commonalities.

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    Related Documents

    IS2104_1_2_Fundamentals of Java.pdf

    Description

    This quiz focuses on creating a class named StringOperations in Java. You'll learn about initializing string variables and understand key string methods. Dive into the fundamentals of string handling in object-oriented programming.

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