2020-01-16 04:07:02 +00:00
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2022-02-15 06:14:58 +00:00
< meta name = "author" content = "Brandon Rozek" >
2020-01-16 04:07:02 +00:00
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< h1 > Lecture for November 13< / h1 >
< h2 > File IO (Cont.)< / h2 >
< p > Last class we talked about reading from files, we can also write to files.< / p >
< h3 > Import necessary libraries< / h3 >
< p > First you must import all of the necessary libraries< / p >
< pre > < code class = "language-java" > // To read
import java.util.Scanner;
import java.io.FileOutputStream;
// To Write
import java.io.FileReader;
import java.io.PrintWriter;
// For Exception Handling
import java.io.IOException;< / code > < / pre >
< p > Then in your main, declare a < code > FileOutputStream< / code > and < code > PrintWriter< / code > < / p >
< pre > < code class = "language-java" > FileOutputStream file;
PrintWriter print;< / code > < / pre >
< h3 > Try-Catch-Finally< / h3 >
< p > Create a try block to open a file for writing< / p >
< pre > < code class = "language-java" > try {
// If the file doesn't exist, it'll create it
file = new FileOutputStream("output.txt");
print = new PrintWriter(file);
} catch (IOException except) {
// Prints out the error message
System.out.println("File error " + except.getMessage());
} < / code > < / pre >
< p > Adding a finally block allows the program to clean up before it closes< / p >
< pre > < code class = "language-java" > try {
file = new FileOutputStream("output.txt");
print = new PrintWriter(file);
} catch (IOException except) {
System.out.println("File error " + except.getMessage());
} finally { // It starts here!
delete file;
delete print;
file.close();
return;
}< / code > < / pre >
< h3 > Write to the file :)< / h3 >
< p > Then you can write the to file!< / p >
< pre > < code class = "language-java" > // Do you notice the following methods?
print.println("Your number is");
print.print("My name is..\n");
print.printf("%s %d", "Hello ", 5);
print.flush(); //Clears the output stream
file.close(); //Closes the file
< / code > < / pre >
< p > Extra Note: Disk fragmentation is a way of cleaning up memory that isn't being used by any of the code on your computer. < / p >
< h2 > Swing Graphics< / h2 >
< h3 > Importing Necessary Libraries< / h3 >
< p > You need to import all the necessary libraries first< / p >
< pre > < code class = "language-java" > import javax.swing.*;
import java.awt.FlowLayout;
import java.awt.event.ActionListener;< / code > < / pre >
< h3 > Changing the class header< / h3 >
< p > Your class file needs to extend < code > JFrame< / code > that way it can use a bunch of the already existent code written for Swing applications< / p >
< pre > < code class = "language-java" > public class firstGUi extends JFrame {
//....< / code > < / pre >
< h3 > Swing Components< / h3 >
< p > Java Swing makes use of what is called Swing Components. These are basic building blocks of GUI items you can add to the screen. For example, a checkbox, a radio button, text field. These are all swing components.< / p >
< p > I wrote a blog post back in the summer which is an overview of them. You can check it out here: < a href = "https://brandonrozek.com/2017/06/java-swing-components/" > https://brandonrozek.com/2017/06/java-swing-components/< / a > < / p >
< p > Inside your < code > firstGUI< / code > class, declare some Swing components you would like to use in the program< / p >
< pre > < code class = "language-java" > public class firstGUI extends JFrame {
JButton button1;
JTextArea area;
JTextField text;
// ....
< / code > < / pre >
< h3 > Constructor< / h3 >
< p > You need to create a constructor for this class that way you can initiate all of the swing component values.< / p >
< pre > < code class = "language-java" > // ...
JButton button1;
JTextArea area;
JTextField text;
// Begin Constructor
firstGUI() {
// Define the components
JLabel name = new JLabel("Enter in your name:");
text = new JTextField("Jennifer", 20); // 20 characters long, default value: Jennifer
area = new JTextArea(10, 10); //Width and Height is 10 characters big
JScrollPane sp = new JScrollPane(area); //Adds a scroll bar for the text area
button1 = new JButton("Press Me");
// Set the Layout
// FlowLayout organizes each of the components top to bottom, left to right
setLayout(new FlowLayout());
// Add the components to the screen
add(name);
add(text);
add(sp); // never add the textarea when surrounded by a ScrollPane
add(button1);
}< / code > < / pre >
< h3 > New Main Method< / h3 >
< p > Finally, you need to create the Main method which will initiate it all< / p >
< pre > < code class = "language-java" > public static void main(String[] args) {
firstGUI myFrame = new firstGUI();
// End the program when the 'x' button (not keyboard) is pressed
myFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
myFrame.setTitle("My title"); // Titles the window
myFrame.pack(); // Packs it all into the frame
myFrame.setVisible(true); // Makes the frame appear on the screen
}< / code > < / pre >
< h3 > Making it interactive< / h3 >
< p > You need to change your class header to the following< / p >
< pre > < code class = "language-java" > public class firstGUI extends JFrame implements ActionListener {
// ...< / code > < / pre >
< p > Then in your class, add the following method< / p >
< pre > < code class = "language-java" > @Override public void actionPerformed(ActionEvent event) {
// Do stuff as a result of an event here
area.append("You Pressed the Button");
}< / code > < / pre >
< p > To make it actually activate as a result of an event. You need to attach it to a swing component.< / p >
< p > For example, I want the code in < code > actionPerformed< / code > to activate in result of a button press.< / p >
< p > Add the following line to your code in the constructor.< / p >
< pre > < code class = "language-java" > //...
button1 = new JButton("Press Me");
button1.addActionListener(this); // New Code
//....< / code > < / pre >
< h3 > Identifying Button Pressed< / h3 >
< p > How do you know which button was pressed in the < code > actionPerformed< / code > method?< / p >
< p > You can use < code > event.getSource()< / code > to find out.< / p >
< p > Example:< / p >
< pre > < code class = "language-java" > @Override public void actionPerformed(ActionEvent event) {
if (event.getSource() == button1) { // Replace button1 with appropriate variable name
// Do things as a result of a specific button being pressed
}
}< / code > < / pre >
< h3 > Summary< / h3 >
< p > To use Swing, do the following steps< / p >
< ol >
< li > Import Libraries< / li >
< li > Declare J___ variables< / li >
< li > New the J___ variables< / li >
< li > Add the J___ variables to the frame< / li >
< li > Add the < code > ActionListener< / code > to the components you wish to monitor< / li >
< / ol >
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