Java and Object-Oriented Programming (OOP)
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Questions and Answers

What does the term 'Write Once, Run Anywhere' (WORA) refer to in Java?

  • Java source code requires a different syntax for each operating system.
  • Java applications can only run on the Java Development Kit (JDK).
  • Java code is compiled into machine code for each operating system.
  • Java applications can be run on multiple operating systems without modification. (correct)

    • Which of the following is NOT a benefit of Object-Oriented Programming (OOP)?

  • Requires the use of more global variables. (correct)
  • Models real-world entities effectively.
  • Supports encapsulation and inheritance.
  • Encourages reusability of code.

    • What is the primary function of the Java compiler?

  • To translate bytecode into high-level source code.
  • To convert Java source code into machine code.
  • To execute bytecode and provide runtime environment.
  • To check syntax and convert code into bytecode. (correct)

    • Which statement about Java Virtual Machine (JVM) is incorrect?

    <p>JVM is platform-dependent and tailored for each operating system. (D)</p> Signup and view all the answers

    What do valid identifiers in Java NOT have to start with?

    <p>A number. (C)</p> Signup and view all the answers

    Which of the following describes a class in Java?

    <p>A blueprint for creating objects with specific attributes and methods. (A)</p> Signup and view all the answers

    Which of these statements accurately describes Java's type system?

    <p>Java is statically typed, with variable types determined at compile time. (B)</p> Signup and view all the answers

    What does encapsulation in OOP primarily promote?

    <p>Hiding the internal states of objects from the outside. (A)</p> Signup and view all the answers

    What does the nextInt() method of the Scanner class do?

    <p>Reads an integer value from the input (B)</p> Signup and view all the answers

    Which line of code correctly prints the value of pi up to two decimal places?

    <p>System.out.printf(&quot;Value of pi: %.2f\n&quot;, pi); (B)</p> Signup and view all the answers

    What will the output be when the age is set to 15 in the following code: if (age >= 18) { System.out.println("You are an adult."); } else { System.out.println("You are a minor."); }?

    <p>You are a minor. (D)</p> Signup and view all the answers

    In the switch statement, if day is equal to 4, what will be the output?

    <p>Invalid day (C)</p> Signup and view all the answers

    Which code snippet correctly demonstrates the use of a for loop?

    <p>for (int i = 0; i &lt; 5; i++) { System.out.println(i); } (C)</p> Signup and view all the answers

    What will be the output of the following code: int[] numbers = {1, 2, 3, 4, 5}; System.out.println(numbers);?

    <p>The address of the array (B)</p> Signup and view all the answers

    What will happen if a 2D array is traversed using the following code snippet? for (int[] row : matrix) { for (int num : row) { System.out.print(num + " "); } }

    <p>It will print all elements in the matrix (A)</p> Signup and view all the answers

    Which of the following function signatures demonstrates method overloading?

    <p>All of the above (D)</p> Signup and view all the answers

    What is the output of greet("Alice", 2); if defined as public static void greet(String name, int times)?

    <p>Hello, Alice! Hello, Alice! (A)</p> Signup and view all the answers

    Which statement accurately describes the difference between syntax and semantics in programming?

    <p>Syntax is the set of rules for writing code, whereas semantics is the meaning of that code. (B)</p> Signup and view all the answers

    What is the primary characteristic of a constant in programming?

    <p>It cannot be modified once assigned a value. (C)</p> Signup and view all the answers

    What will happen if you perform a narrowing conversion without casting?

    <p>A compile-time error will occur. (A)</p> Signup and view all the answers

    Which of the following correctly describes the behavior of the 'break' statement in loops?

    <p>It exits the nearest enclosing loop. (D)</p> Signup and view all the answers

    What is the purpose of garbage collection in programming?

    <p>To free up memory from objects that have not been referenced. (A)</p> Signup and view all the answers

    In a two-dimensional array, how are elements typically organized?

    <p>As an array of arrays. (B)</p> Signup and view all the answers

    What will the output of the following code segment be if 'x' is equal to 5? String result = (x > 3) ?"Greater" : "Lesser"; System.out.println(result);

    <p>Greater (C)</p> Signup and view all the answers

    Which of the following statements about reference variables is incorrect?

    <p>They always refer to a unique object. (B)</p> Signup and view all the answers

    What does the 'equals()' method do when comparing strings?

    <p>It compares the content of the strings. (B)</p> Signup and view all the answers

    Which of the following statements about loops is true?

    <p>A 'do-while' loop can never execute zero times. (A)</p> Signup and view all the answers

    In Java, which primitive data type can represent a boolean value?

    <p>boolean (C)</p> Signup and view all the answers

    Which type of variables can hold values that can be changed during execution?

    <p>Variables (B)</p> Signup and view all the answers

    When using 'System.out.printf()', which of the following is a correct format specifier for an integer?

    <p>%d (D)</p> Signup and view all the answers

    What will happen if you assign a string literal to a variable declared as an integer?

    <p>A compile-time error will occur. (C)</p> Signup and view all the answers

    Study Notes

    Java and Object-Oriented Programming (OOP)

    • Java, developed by Sun Microsystems (now Oracle) in 1995, aims for platform independence (WORA).

    • Evolved from Oak, designed for embedded systems.

    • Object-Oriented Programming (OOP): Enhances modularity, reusability, and maintainability. Models real-world entities using classes and objects. Supports encapsulation, inheritance, and polymorphism.

    • Classes: Blueprints for objects, defining attributes and behaviors.

    • Objects: Instances of classes, representing real-world entities with state (attributes) and behavior (methods).

    • Compiled vs. Interpreted Languages: Java compiles to bytecode—interpreted by the Java Virtual Machine (JVM).

    • Compiler (Java): Converts Java code into bytecode (.class files), checks syntax, and optimizes.

    • Interpreter (JVM): Executes bytecode, providing a runtime environment.

    • Platform Independence: Bytecode runs on any system with a JVM.

    • Performance: Bytecode is optimized for execution on the JVM.

    • Identifiers: Names for variables, methods, and classes. Rules: start with a letter, underscore (_), or dollar sign ($); cannot be reserved words.

    • Reserved Words: Keywords with predefined meanings (e.g., class, public, static).

    • Valid Identifiers: Examples: myVariable, count1, _name.

    • Declaring vs. Instantiating: Declare a variable or object (e.g., int x;) and instantiate an object using new (e.g., MyClass obj = new MyClass();).

    • Java is statically-typed: Variable types determined at compile time.

    • Designing a Class: Defines attributes (e.g., String name) and behaviors (e.g., void speak()).

    Java Basics

    • Errors:

      • Compiler errors: Syntax issues (e.g., missing semicolon).
      • Runtime errors: Occur during execution (e.g., division by zero).
      • Logical errors: Incorrect program logic (e.g., wrong output).

    • Syntax vs. Semantics: Syntax are code rules; Semantics are code meaning.

    • Variables vs. Constants: Variables change value; constants don't (e.g., final int MAX = 100;).

    • Scope of a Variable: Where a variable can be accessed (local, instance, class).

    • Keywords:

      • final: Prevents modification or inheritance.
      • static: Belongs to the class, not the instance.

    • Primitives: Basic data types like int, double, char, boolean.

      • Memory sizes (examples): int (4 bytes), double (8 bytes).

    • Legal Assignment of Literals: Assigning values to variables (e.g., int x = 10;).

    • Type Conversion:

      • Widening: Automatic conversion (e.g., int to double).
      • Narrowing: Requires casting (e.g., double to int).

    • Casting: Explicitly converting types (e.g., int x = (int) 3.14;).

    • Purpose of Multiple Primitive Types: Optimize memory usage and precision.

    • Primitive Operations: Arithmetic (+, -, *, /, %).

      • Order of Operations: PEMDAS.
      • Assignment Operators: =, +=, -=, *=, etc.

    • Strings: Immutable sequences of characters.

      • String methods: length(), charAt(), substring(), etc.
      • String constant pool: Stores unique string literals).

    • Reference Variables: Point to objects in memory.

      • Aliases: Multiple references to the same object.

    • Garbage Collection: Automatically frees memory from unused objects.

    Input/Output and Formatting

    • Scanner: Reads input from the console. Methods: nextLine(), nextInt(), etc..

    • Packages: java.lang (String, System); java.util (Scanner, Arrays).

    • Formatting:

      • System.out.printf(): Formatted output.
      • String.format(): Format strings.
      • DecimalFormat: Format numbers.

    Decision-Making Statements

    • Conditional Statements:

      • if, else if, else
      • Ternary operator: Shorthand for if-else.
      • switch: Multi-way branching.
      • break: Exits switch.
      • default: Executes if no case matches.

    • String Comparison: equals(), compareTo().

    • Logical Operators: && (AND), || (OR), ! (NOT).

    Iteration

    • Loops:

      • while: Repeats while a condition is true.
      • do-while: Executes at least once.
      • for: Compact loop with initialization, condition, and update.

    • break: Exits the loop.

    • continue: Skips to the next iteration.

    Arrays

    • Arrays: Fixed-size collections.

      • Default values: 0 for numbers, null for objects.

    • 2D Arrays: Arrays of arrays.

      • Row-major vs. column-major traversal.

    • Wrapper Classes: (e.g., Integer, Double) for primitives.

    • Arrays Class: Utility methods (e.g., sort(), binarySearch()).

    Methods

    • Writing Methods: Defining returnType methodName(parameters).

    • Method Overloading: Multiple methods with the same name but different parameters.

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    Description

    This quiz explores the fundamentals of Java and Object-Oriented Programming (OOP). It covers key concepts such as classes, objects, and the distinctions between compiled and interpreted languages. Dive into the foundational principles that make Java a strong option for platform-independent development.

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