Java Basic Syntax and Identifiers
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Questions and Answers

Which is considered a legal identifier in Java?

  • 123abc
  • -salary
  • my class
  • $salary (correct)

Which of the following correctly demonstrates the naming convention for Java class names?

  • public class MyFirstJavaClass (correct)
  • public class myFirstjavaclass
  • public Class myFirstJavaClass
  • public class myfirstjavaclass

What modifier would you use to prevent a method from being overridden in subclasses?

  • abstract
  • final (correct)
  • protected
  • default

Which statement about Java arrays is correct?

<p>Java arrays must be initialized with a fixed size. (D)</p> Signup and view all the answers

What is the primary benefit of using enums in Java?

<p>They restrict a variable to have predefined values. (B)</p> Signup and view all the answers

What must be true for the Java program file name?

<p>It must match the class name exactly. (A)</p> Signup and view all the answers

Which of the following statements about objects is true?

<p>An object is an instance of a class. (A)</p> Signup and view all the answers

What is the primary purpose of a method in a Java class?

<p>To perform actions and manipulate data. (D)</p> Signup and view all the answers

Which of the following describes a class in Java?

<p>A blueprint that defines objects' states and behaviors. (A)</p> Signup and view all the answers

What is the correct format for the main method in a Java program?

<p>public static void main(String[] args) (D)</p> Signup and view all the answers

Which of the following is NOT a requirement for identifiers in Java?

<p>They must not use uppercase letters. (B)</p> Signup and view all the answers

What does an instance variable represent in a Java object?

<p>A unique property of the object. (D)</p> Signup and view all the answers

Which of the following describes the nature of a Java class?

<p>It describes the behaviors and states of its objects. (B)</p> Signup and view all the answers

Flashcards

Java Program

A collection of objects that interact with each other through methods.

Object

An instance of a class, possessing its own state and behaviour.

Class

A blueprint or template that defines the characteristics and actions of objects.

Method

A function or procedure that encapsulates a specific action or behaviour.

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Instance Variables

Unique variables that belong to an object, defining its current state.

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Program File Name

The name of a Java program file must match the name of its main class, with the '.java' extension.

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public static void main(String args[])

This method is the starting point for any Java program execution.

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Java Identifiers

Names used for classes, variables, and methods in Java.

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Case Sensitivity in Java

In Java, identifiers (names for classes, variables, and methods) are case-sensitive, meaning 'Hello' and 'hello' are treated as distinct names.

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Java Class Naming Conventions

Class names in Java follow a specific naming convention: the first letter is capitalized, and subsequent words are also capitalized (e.g., MyFirstJavaClass).

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Java Method Naming Conventions

Method names in Java start with a lowercase letter, and subsequent words are capitalized (e.g., myMethodName).

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Java Modifiers

Java modifiers are keywords that alter the behavior of classes, methods, or variables. Access modifiers control visibility (e.g., public, private), while non-access modifiers add extra features (e.g., final, abstract).

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Java Enums

Enums (enumerations) in Java restrict a variable to a fixed set of predefined values. For example, a 'size' variable could only be 'small', 'medium', or 'large' using an enum.

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Study Notes

Java Basic Syntax

  • A Java program consists of objects that communicate by invoking methods.
  • Object: Has states (e.g., color, name) and behaviors (e.g., barking, eating). An instance of a class.
  • Class: A template/blueprint defining object behavior/state.
  • Methods: Behaviors within a class, containing logic and data manipulation.
  • Instance Variables: Unique attributes defining an object's state.

Java Identifiers

  • Java components (classes, variables, methods) require names called identifiers.
  • Identifiers start with a letter (a-z, A-Z), underscore (_), or dollar sign ($).
  • Subsequent characters can be letters, numbers, underscores, or dollar signs.
  • Keywords cannot be used as identifiers.
  • Identifiers are case-sensitive (e.g., hello and Hello are different).
  • Examples of valid identifiers: age, $salary, _value, 1_value.
  • Examples of invalid identifiers: 123abc, -salary.

Program Files

  • Program file name should match the class name.

  • Append ".java" to the filename.

  • Java programs execute from the main() method (mandatory).

Java Modifiers

  • Modifiers are used to control class, method, and other functionalities.
  • There are access modifiers and non-access modifiers.
  • Access Modifiers: Control access levels (default, public, protected, private).
  • Non-access Modifiers: Define properties (final, abstract, strictfp).

Java Arrays

  • Arrays store multiple variables of the same type.
  • An array itself is an object stored in the heap.
  • Data structure for storing multiple elements in a sequence

Java Enums

  • Introduced in Java 5.0.
  • Restricts a variable to a predefined set of values (enum values).
  • Reduces bugs in program code (e.g., restricting juice sizes to small, medium, and large).

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Description

This quiz covers the fundamental concepts of Java basic syntax, focusing on objects, classes, methods, and identifiers. It explains the rules for naming identifiers and highlights the importance of adhering to Java's case-sensitivity and naming conventions. Test your understanding of these core principles of Java programming.

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