Java中的JTextArea中的append数据如何获取？

Question

I am using this code to show text in a JTextArea :

jTextArea1.setText(jTextArea1.getText() + text + "\r\n");
jTextArea1.repaint();

But it shows an exception:

java.lang.NullPointerException

Answer 1

You never instantiated your JTextArea . Also, you might want to check out JTextArea#append .

Answer 2

jTextArea1.setText(jTextArea1.getText() + text + "\r\n");

StringBuilder sb = new StringBuilder();
if(jTextArea1.getText().trim().length() > 0){
    sb.append(jTextArea1.getText().trim());
}
sb.append(text).append("\r\n");

jTextArea1.setText(sb.toString());

Above two friends gave you answer. I want to explain it. Because first times I also met that problem. I solved that, but today solve as above code snippet.

Answer 3

The following code adds text to the text area. Note that the text system uses the '\n' character internally to represent newlines; for details, see the API documentation for DefaultEditorKit.

private final static String newline = "\n";
...
textArea.append(text + newline);

Source

Answer 4

As Jeffrey pointed out, you have to create an object instance before you call non-static methods on it. Otherwise, you will get a NullPointerException . Also note that appending a text to a JTextArea can be done easily by calling its JTextArea.append(String) method. See the following example code for more detail.

package test;

import javax.swing.JFrame;
import javax.swing.JTextArea;

public class Main {
  public static void main(String[] args) {
    Main m = new Main();
    m.start();
  }
  private void start() {
    JTextArea ta = new JTextArea();
    ta.append("1\n");
    ta.append("2\n");
    ta.append("3\n");
    JFrame f = new JFrame();
    f.setSize(320, 200);
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    f.getContentPane().add(ta);
    f.setVisible(true);
  }
}