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