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1. In Java a class can only directly inherit for a single parent class. Explain why this is not a limitation. Give an example

1. In Java a class can only directly inherit for a single parent class. Explain why this is not a limitation. Give an example

Database System Concepts
Database System Concepts
7th Edition
ISBN:9780078022159
Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Chapter1: Introduction
Section: Chapter Questions
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1. In Java a class can only directly inherit for a single parent class. Explain why this is not a limitation. Give an example

2. What would be an example of overriding a method? In terms of inheritance, why is it important to be able to override a method?

3. Consider the following Java classes. Assuming that all of these classes are in the same directory. What will be the output when TestClassC is compiled and run.

```java public class ClassC extends ClassB { public ClassC() { super(); } public String toString() { String temp = ""; for (int i = 0; i < strings.size(); i++) { temp += "#" + strings.get(i) + "#"; if (i < strings.size() - 1) { temp += "\n"; } } return temp; } } class TestClassC { public static void main(String[] args) { ClassC myList = new ClassC(); myList.add("STOP"); myList.add("GO"); myList.add("TURN"); System.out.print(myList); System.out.println("all done"); } } ``` ### Explanation: - **ClassC**: This class extends another class called `ClassB`. It contains a constructor and a `toString` method. - **Constructor**: Calls the constructor of the superclass `ClassB` using `super()`. - **toString Method**: Iterates over a list `strings`, formatting each string with `#` symbols and separating entries with newline characters `\n`. The method returns this formatted string. - **TestClassC**: This class contains the `main` method for testing. - **main Method**: - Creates an instance of `ClassC` named `myList`. - Adds three strings: "STOP", "GO", and "TURN" to `myList`. - Prints the result of `myList` using `System.out.print`. - Prints "all done" using `System.out.println`. This example demonstrates basic inheritance, object creation, string manipulation, and printing in Java.
Transcribed Image Text:```java public class ClassC extends ClassB { public ClassC() { super(); } public String toString() { String temp = ""; for (int i = 0; i < strings.size(); i++) { temp += "#" + strings.get(i) + "#"; if (i < strings.size() - 1) { temp += "\n"; } } return temp; } } class TestClassC { public static void main(String[] args) { ClassC myList = new ClassC(); myList.add("STOP"); myList.add("GO"); myList.add("TURN"); System.out.print(myList); System.out.println("all done"); } } ``` ### Explanation: - **ClassC**: This class extends another class called `ClassB`. It contains a constructor and a `toString` method. - **Constructor**: Calls the constructor of the superclass `ClassB` using `super()`. - **toString Method**: Iterates over a list `strings`, formatting each string with `#` symbols and separating entries with newline characters `\n`. The method returns this formatted string. - **TestClassC**: This class contains the `main` method for testing. - **main Method**: - Creates an instance of `ClassC` named `myList`. - Adds three strings: "STOP", "GO", and "TURN" to `myList`. - Prints the result of `myList` using `System.out.print`. - Prints "all done" using `System.out.println`. This example demonstrates basic inheritance, object creation, string manipulation, and printing in Java.
The image contains Java code defining two classes, `ClassA` and `ClassB`. Below is the transcription and explanation of the code: ### ClassA ```java import java.util.ArrayList; public class ClassA { protected ArrayList<String> strings; public ClassA() { strings = new ArrayList<String>(); } public void add(String s) { strings.add(s); } public String toString() { String temp = ""; for (String s : strings) { temp += s + "\n"; } return temp; } } ``` #### Explanation: 1. **Import Statement**: The `ArrayList` from `java.util` package is imported to store strings. 2. **Class Declaration**: `ClassA` is a public class. 3. **Field**: A protected `ArrayList<String>` named `strings` is declared. This allows subclasses to access it. 4. **Constructor**: Initializes `strings` as a new `ArrayList`. 5. **Methods**: - `add(String s)`: Adds a string `s` to the `strings` list. - `toString()`: Returns all stored strings concatenated with a newline between each. ### ClassB ```java public class ClassB extends ClassA { public ClassB() { super(); } public void add(String s) { strings.add(s.toLowerCase()); } } ``` #### Explanation: 1. **Class Declaration**: `ClassB` is a public class that extends `ClassA`, inheriting its fields and methods. 2. **Constructor**: Calls the superclass (ClassA) constructor using `super()`. 3. **Overridden Method**: - `add(String s)`: Overrides the `add` method from `ClassA` to store the strings in lowercase. ### Summary - **Inheritance**: `ClassB` inherits from `ClassA` and modifies behavior by overriding a method. - **`add` Method Difference**: `ClassA` stores strings as they are, while `ClassB` converts them to lowercase before storing. - **Access Levels**: The `protected` access level in `ClassA` allows `ClassB` to access the `strings` list directly. This code demonstrates basic inheritance, method overriding, and the use of Java collections.
Transcribed Image Text:The image contains Java code defining two classes, `ClassA` and `ClassB`. Below is the transcription and explanation of the code: ### ClassA ```java import java.util.ArrayList; public class ClassA { protected ArrayList<String> strings; public ClassA() { strings = new ArrayList<String>(); } public void add(String s) { strings.add(s); } public String toString() { String temp = ""; for (String s : strings) { temp += s + "\n"; } return temp; } } ``` #### Explanation: 1. **Import Statement**: The `ArrayList` from `java.util` package is imported to store strings. 2. **Class Declaration**: `ClassA` is a public class. 3. **Field**: A protected `ArrayList<String>` named `strings` is declared. This allows subclasses to access it. 4. **Constructor**: Initializes `strings` as a new `ArrayList`. 5. **Methods**: - `add(String s)`: Adds a string `s` to the `strings` list. - `toString()`: Returns all stored strings concatenated with a newline between each. ### ClassB ```java public class ClassB extends ClassA { public ClassB() { super(); } public void add(String s) { strings.add(s.toLowerCase()); } } ``` #### Explanation: 1. **Class Declaration**: `ClassB` is a public class that extends `ClassA`, inheriting its fields and methods. 2. **Constructor**: Calls the superclass (ClassA) constructor using `super()`. 3. **Overridden Method**: - `add(String s)`: Overrides the `add` method from `ClassA` to store the strings in lowercase. ### Summary - **Inheritance**: `ClassB` inherits from `ClassA` and modifies behavior by overriding a method. - **`add` Method Difference**: `ClassA` stores strings as they are, while `ClassB` converts them to lowercase before storing. - **Access Levels**: The `protected` access level in `ClassA` allows `ClassB` to access the `strings` list directly. This code demonstrates basic inheritance, method overriding, and the use of Java collections.
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