Questions and Answers
Match the following Java concepts with their descriptions:
Multidimensional Array (2D) = Data stored in row and column based index Constructors = Block of code similar to a method Inheritance = Creating new classes built upon existing classes Types of Java constructors = Default constructor and Parameterized constructor
Match the following rules for creating Java constructors with their descriptions:
Constructor name must be the same as its class name = Naming requirement for constructors A Constructor must have no explicit return type = Return type specification for constructors A Java constructor cannot be abstract, static, final, and synchronized = Restrictions on constructor modifiers Why we use inheritance in java? = Reasons for utilizing inheritance in Java
Match the following types of Java constructors with their characteristics:
Default constructor = Constructor with no arguments Parameterized constructor = Constructor with parameters specified during object creation Parent class = Class from which another class inherits properties Child class = Class that inherits properties from another class
Match the following inheritance types with their definitions:
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What is the purpose of a constructor in Java?
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Which of the following is NOT a valid rule for creating a constructor in Java?
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In the context of inheritance, what is the purpose of method overriding?
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What type of inheritance is described by the following statement: 'A class having more than one parent class but at different levels'?
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Which of the following is a valid reason for using inheritance in Java?
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A Java constructor must have an explicit return type.
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Inheritance in Java allows creating new classes based on existing classes.
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Parameterized constructors in Java have default values if parameters are not provided.
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Multilevel Inheritance in Java refers to a class having more than one parent class at the same level.
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Java constructors can be declared as static.
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What are the rules for creating a Java constructor?
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How is inheritance defined in Java and why is it used?
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What are the types of Java constructors?
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What is Multilevel Inheritance in Java?
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When is a Java constructor called?
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Study Notes
Object-Oriented Programming (OOP) in Java
- OOP is a programming style that increases program flexibility and maintainability.
- It allows for easy reuse of objects in other programs and manages software complexity.
- OOP concepts in Java include:
- Class
- Object
- Abstraction
- Inheritance
- Polymorphism
- Encapsulation/Data Hiding
Classes and Objects
- A class is a collection of objects and is a logical entity.
- A class can contain:
- Fields
- Methods
- Constructors
- Blocks
- Nested classes
- An object is an instance of a class and has three characteristics:
- State (represents the value of an object)
- Behavior (represents the functionality of an object)
- Identity (implemented via a unique ID)
- Object definitions:
- A real-world entity
- A runtime entity
- An instance of a class
Methods in Java
- A method is a collection of statements that perform a specific task and return a result to the caller.
- Reasons to use methods:
- To perform a specific task
- To return a result to the caller
- Types of Java methods:
- Standard Library Methods (built-in methods, e.g. print(), println(), round(), sqrt())
- User-defined Methods (defined inside a class, per requirement)
Arrays in Java
- An array is used to store a collection of variables of the same type.
- Array advantages:
- Code optimization
- Random access
- Array disadvantages:
- Size limit (fixed size, does not grow at runtime)
- Types of arrays in Java:
- Single Dimensional Array
- Multidimensional Array
- Syntax to declare an array in Java:
-
dataType[] arr; -
dataType []arr; -
dataType arr[];
-
- Creating arrays:
-
dataType[] arr = new dataType[arraySize]; -
dataType[] arr = {value0, value1, ..., valuek};
-
Jump Statements in Java
- Java supports three jump statements:
- Break (terminates the execution of the nearest looping statement or switch statement)
- Continue (pushes the next repetition of the loop to take place, hopping any code between itself and the conditional expression that controls the loop)
- Return (transfers control from one method to the method that called it)
Constructors in Java
- A constructor is a block of code similar to a method.
- When is a constructor called?
- Every time an object is created using the new () keyword.
- Rules for creating a Java constructor:
- Constructor name must be the same as its class name.
- A constructor must have no explicit return type.
- A Java constructor cannot be abstract, static, final, and synchronized.
- Types of Java constructors:
- Default constructor
- Parameterized constructor
Inheritance in Java
- Inheritance is used to create new classes that build upon existing classes.
- There are two classes:
- Parent class
- Child class
- Why use inheritance in Java?
- For method overriding
- For code reusability
- Inheritance is further classified into four types:
- Multilevel Inheritance (a class having more than one parent class but at different levels)
