Analyze text boxes and text areas in Java graphical programming

In a graphical interface, text boxes and text areas are components for information input and output.
Text box

A text box (JTextField) is a box in the interface that is used to input and output a line of text. JTextField class is used to create text boxes. The interface associated with text boxes is ActionListener.

The basic content of the text box handler is as follows:

• Declare a text box name.
• Create a text box object.
• Add a text box object to a container.
• Register a monitor for the text box object that needs to be controlled and listen for the end of the input of the text box (that is, enter the Enter key) event.
• A method to handle text box events, completes the judgment and processing of intercepted events.

The main constructor methods of JTextField class:

• JTextField(), the character length of the text box is 1.
• JTextField(int columns), the initial value of the text box is an empty string, and the character length of the text box is set to columns.
• JTextField(String text), a string whose initial value of the text box is text.
• JTextField(String text,int columns); The initial value of the text box is text, and the character length of the text box is columns.

Other methods of JTextField class:

• setFont(Font f), set font
• setText(String text), set text in the text box
• getText(), get the text in the text box.
• setEditable(boolean), specifies the editability of the text box, default to true, editable.
• setHorizontalAlignment(int alignment) sets text alignment. The alignment methods are: JTextField.LEFT, JTextField.CENTER, JTextField.RIGHT.
• requestFocus(), set the focus.
• addActionListener(ActionListener ), sets an action monitor for the text box, and specifies that the ActionListener object receives the input end action event that occurs on the text box.
• removeActionListener(ActionListener) Removes the text box monitor.
• getColumns(), returns the number of columns in the text box.
• getMinimumSize(), returns the minimum size required for the text box.
• getMinimumSize(int), returns the minimum size required for the text box in the specified number of characters.
• getPreferredSize(), returns the size the text box wants to have.
• getPreferredSize(int), returns the size that the text box wants to have when the number of characters is specified.

[Example] The applet has two text boxes. One text is used to enter an integer, and another text box displays the squared value of this integer. The program uses a string to convert the basic type method Long.parseLong(text1.getText()), reads the string in text box text1, and converts it into an integer. The program uses an instance of the Sqr class as a monitor, but in order for the monitor to access the variables of the main class, the variables in the main class are declared as class variables and access permissions are not set (see the source file).

The password box (JPasswordField) is a single-line input component, which is basically similar to JTextField. The password box has an additional blocking function, which means that when input, it will be output as another specified character (usually * character). In addition to the text box methods introduced earlier, there are some commonly used methods for password boxes:

• getEchoChar(), returns the echo character of the password.
• setEchoChar(char), sets the echo character of the password box.

Text area

The text area (JTextArea) is an area in the form where text is placed. The main difference between a text area and a text box is that the text area can store multiple lines of text. The JTextArea class in the javax.swing package is used to create text areas. There are no events for the JTextArea component.

The basic content of the text area processing program is as follows:

• Declare a text area name.
• Create a text area object.
• Add text area objects to a container.

The main constructor methods of JTextArea class:

• JTextArea() creates a text area object with the default number of columns and rows.
• JTextArea(String s), creates a text area object with s as the initial value.
• JTextArea(Strings ,int x,int y), with s as the initial value, the number of rows is x and the number of columns is y, create a text area object.
• JTextArea(int x,int y) creates a text area object with the number of rows as x and the number of columns as y.

Other common methods of the JTextArea class:

• setText(String s), sets the display text and clears the original text at the same time.
• getText(), get the text in the text area.
• insert(String s,int x), insert the specified text at the specified position.
• replace(String s,int x,int y), replace the text starting from the x position to ending at the y position with the given one.
• append(String s), append text to the text area.
• getCarePosition(), get the position of the active cursor in the text area.
• setCarePosition(int n), set the position of the active cursor.
• setLineWrap(boolean b), set automatic line wrapping, default, no automatic line wrapping.

The following code creates a text area and sets it to automatically wrap it.

 JTextArea textA = new JTextArea("I am a text area", 10, 15); textA.setLineWrap(true);//Set automatic line wrap

When there is a lot of content in the text area and cannot be displayed in the text area, you can attach a scroll bar to the text area. Setting a scrollbar for the text area allows the following code:

 JTextArea ta = new JTextArea(); JScrollPane jsp = new JScrollPane(ta);//Add scrollbars to the text area

In the GUI, commonly used text boxes and text areas implement data input and output. If you use text area input, you usually set another data input completion button. When the data input is finished, click this button. The event handler uses the getText() method to read string information from the text area. For situations where text boxes are used as input, the last input carriage return character can inspire the input completion event, usually without setting another button. The event handler can use the word analyzer to analyze numbers, and then use the string conversion method to obtain the input numerical value. For output, the program first converts the value into a string, and then outputs the data to a text box or text area through the setText() method.

[Example] The applet sets a text area, a text box and two buttons. The user enters an integer sequence in the text area, clicks the sum button, the program sums the integer sequence in the text area, and outputs the sum in the text box. Click the second button to clear the contents in the text area and text boxes.

 import java.util.*;import java.applet.*;import java.awt.*;import javax.swing.*;import java.awt.event.*;public class J509 extends App let implements ActionListener{ JTextArea textA; JTextField textF ;JButton b1,b2; public void init(){ setSize(250,150); textA=new JTextArea("",5,10); textA.setBackground(Color.cyan); textF=new JTe xtField("",10); textF.setBackground(Color.pink); b1=new JButton("Sum"); b2=new JButton("Restart"); textF.setEditable(false); b1.addActionListener(this); b 2.addActionListener(this ); add(textA); add(textF); add(b1); add(b2); } public void actionPerformed(ActionEvent e){ if(e.getSource()==b1){ String s=textA.get Text( ); StringTokenizer tokens=new StringTokenizer(s); //Use the default separator set: spaces, line breaks, Tab conform to carriage return as separator int n=tokens.countTokens(),sum=0,i; for(i= 0;i<=n-1;i++){ String temp=tokens.nextToken();//Pick a data sum+=Integer.parseInt(temp); } textF.setText(""+sum); } else if(e.getSource()==b2){ textA.setText(null); textF.setText(null); } }}

[Example] The applet calculates all numbers from the starting integer to the ending integer that are factor multiples. The applet container uses GridLayout layout to divide the interface into 3 rows, the first row is the label, and the second row and the third row are two Panels. Two Panel container classes Panel1 and Panel2 are designed, and they are divided by GridLayout layout. Panel1 has 1 row and 6 columns, and Panel2 has 1 row and 4 columns. Then add the components generated by the label and container classes Panel1 and Panel2 to the corresponding position of the window.

 import java.applet.*;import javax.swing.*;import java.awt.*;import java.awt.event.*;class Panel1 extends JPanel{ JTextField text1,text2,t ext3; Panel1(){//Construction method . When creating a Panel object, the Panel is initialized to have three labels //three text boxes, with the layout as GridLayout(1,6) text1=new JTextField(10); text2=new JTextField(10); text3=new JTextField(10); );setLayout(new GridLayout(1,6)); add(new JLabel("start number", JLabel.RIGHT));add(text1); add(new JLabel("terminal number", JLabel.RIGHT)) ;add(text2); add(new JLabel("factor",JLabel.RIGHT));add(text3); }}class Panel2 extends JPanel{//Extend Panel class JTextArea text;JButton Button; Panel2 (){// Constructing method. When creating a Panel object, the Panel is initialized to have a tag // a text box, with the layout as GridLayout(1,4) text=new JTextArea(4,10); text.setLineWrap(true); JScrollPane jsp=new JScroll Pane( text); Button=new JButton("Start calculation"); setLayout(new GridLayout(1,4)); add(new JLabel("Computation result:",JLabel.RIGHT)); add(jsp); add(new Label());add(Button); }}public class J510 extends Applet implements ActionListener{ Panel1 panel1; Panel2 panel2; public void init(){ setLayout(new Gr idLayout(3,1)); setSize(400,200);panel1= new Panel1();panel2=new Panel2(); add(new JLabel("calculate the number from the start number to the end number is a factor multiple",JLabel.CENTER)); add(panel1);add(panel2); ( panel2.Button).addActionListener(this); } public void actionPerformed(ActionEvent e){ if(e.getSource()==(panel2.Button)){ long n1,n2,f,count=0 ; n1=Long. parseLong(panel1.text1.getText()); n2=Long.parseLong(panel1.text2.getText()); f=Long.parseLong(panel1.text3.getText()); for(long i=n1;i< =n2;i++){ if(i%f==0) panel2.text.append(String.valueOf(i)+""); } } }}