Problems Flashcards
Text I/O Read and Write File a File Example
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
public class TextFileIOExample {
public static void main(String[] args) {
String fileName = "textfile.txt";
try (BufferedWriter writer = new BufferedWriter(new FileWriter(fileName))) {
writer.write("Hello, this is a text file example.\n");
writer.write("Writing some text to demonstrate text file I/O.\n");
} catch (IOException e) {
e.printStackTrace();
}
try (BufferedReader reader = new BufferedReader(new FileReader(fileName))) {
String line;
while ((line = reader.readLine()) != null) {
System.out.println(line);
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
Binary I/O Read and Write a File Example
import java.io.*;
public class BinaryFileIOExample {
public static void main(String[] args) {
String fileName = "binaryfile.dat";
try (DataOutputStream dos = new DataOutputStream(new FileOutputStream(fileName))) {
dos.writeInt(42);
dos.writeDouble(3.14);
dos.writeUTF("Binary file example.");
} catch (IOException e) {
e.printStackTrace();
}
try (DataInputStream dis = new DataInputStream(new FileInputStream(fileName))) {
int intValue = dis.readInt();
double doubleValue = dis.readDouble();
String stringValue = dis.readUTF();
System.out.println("Int value: " + intValue);
System.out.println("Double value: " + doubleValue);
System.out.println("String value: " + stringValue);
} catch (IOException e) {
e.printStackTrace();
}
}
}
Read input from the console and write it to a file using Scanner and FileWriter
import java.io.FileWriter;
import java.io.IOException;
import java.util.Scanner;
public class ConsoleInputFileOutput {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
FileWriter fileWriter = null;
try {
System.out.print("Enter the file name: ");
String fileName = scanner.nextLine();
fileWriter = new FileWriter(fileName);
System.out.println("Enter text (type 'exit' to stop):");
String line;
while (!(line = scanner.nextLine()).equalsIgnoreCase("exit")) {
fileWriter.write(line + "\n");
}
System.out.println("Data has been written to the file.");
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (fileWriter != null) {
fileWriter.close();
}
} catch (IOException e) {
e.printStackTrace();
}
// Close the scanner
scanner.close();
}
}
}
Fully Loaded Constructor
public class Person {
private String name;
private int age;
public Person(String name, int age) {
this.name = name;
this.age = age;
}
}
Mutator Method
public void setAge(int age) {
this.age = age;
}
Copy Constructor
public class Person {
private String name;
private int age;
public Person(String name, int age) {
this.name = name;
this.age = age;
}
public Person(Person other) {
this.name = other.name;
this.age = other.age;
}
}
toString Method
@Override
public String toString() {
return "Person[name=" + name + ", age=" + age + "]";
}
Accessor
public int getAge() {
return age;
}
Main Method
public class Main {
public static void main(String[] args) {
// Your main code here
}
}
Derived Class
public class Student extends Person {
private int studentId;
public Student(String name, int age, int studentId) {
super(name, age);
this.studentId = studentId;
}
}
Instance Variables
public class Example {
private int variable1; private String variable2;
}
Accessors and Mutators
public int getVariable1() {
return variable1;
}
public void setVariable1(int variable1) {
this.variable1 = variable1;
}
public String getVariable2() {
return variable2;
}
public void setVariable2(String variable2) {
this.variable2 = variable2;
}
Override toString
@Override
public String toString() {
return "Example[variable1=" + variable1 + ", variable2=" + variable2 + "]";
}
Hierarchy and Polymorphism
public abstract class Shape {
public abstract double calculateArea();
}
public class Circle extends Shape {
private double radius;
public Circle(double radius) {
this.radius = radius;
}
@Override
public double calculateArea() {
return Math.PI * radius * radius;
}
}
Define and Use Recursive Method
public class RecursiveExample {
public int factorial(int n) {
if (n == 0 || n == 1) {
return 1;
} else {
return n * factorial(n - 1);
}
}
}
Class and Object Example
class Car {
}
Car myCar = new Car();
Composition Example
class Component {}
class Composition {
private Component component;
}
Inheritance Example
class Parent {}
class Child extends Parent {}
Abstract Class and Interface Example
abstract class AbstractClass {
abstract void performAction();
}
class ConcreteClass extends AbstractClass {
void performAction() {
System.out.println("Performing concrete action");
}
}
Exception Handling Example
try {
throw new IOException("Input/Output Exception");
} catch (IOException e) {
System.out.println("Caught IOException: " + e.getMessage());
}
GUI Basics Example
import javax.swing.*;
import java.awt.*;
JFrame frame = new JFrame(“GUI Example”);
JButton button = new JButton(“Click Me”);
frame.add(button);
Recursion Example
static int calculateFactorial(int n) {
return n == 0 || n == 1 ? 1 : n * calculateFactorial(n - 1);
}
File I/O Example
try (PrintWriter writer = new PrintWriter(“output.txt”)) {
writer.println("Hello, World!");
} catch (IOException e) {
System.out.println("Error writing to file: " + e.getMessage());
}
Generics Example
class Box<T> {</T>
private T content;
public void put(T item) {
this.content = item;
}
public T get() {
return content;
}
}
Box<String> stringBox = new Box<>();</String>
stringBox.put(“Hello”);
String greeting = stringBox.get();
Case Convertor
import javax.swing.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
public class CaseConverter extends JFrame {
private JTextField inputField;
private JTextField outputField;
public CaseConverter() {
super("Case Converter");
inputField = new JTextField(20);
outputField = new JTextField(20);
outputField.setEditable(false);
JButton convertButton = new JButton("Convert");
convertButton.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
convertText();
}
});
setLayout(new BoxLayout(getContentPane(), BoxLayout.Y_AXIS));
add(new JLabel("Input Text:"));
add(inputField);
add(new JLabel("Converted Text:"));
add(outputField);
add(convertButton);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
pack();
setLocationRelativeTo(null);
}
private void convertText() {
String inputText = inputField.getText();
String convertedText = "";
convertedText = inputText.toUpperCase();
outputField.setText(convertedText);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
@Override
public void run() {
new CaseConverter().setVisible(true);
}
});
} }
