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2022-02-15 01:14:58 -05:00
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2020-01-15 23:07:02 -05:00
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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>
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