blocks|key|79813|text|为此，您需要为JTextField添加change+listener+(对文本中的更改做出反应的DocumentListener+)，并且在actionPerformed()中，您需要根据JTextfield是否为空将loginButton更新为enabled/disabled。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|79814|下面是我从这个thread中找到的东西。|79815|yourJTextField.getDocument().addDocumentListener(new+DocumentListener()+{
++public+void+changedUpdate(DocumentEvent+e)+{
++++changed();
++}
++public+void+removeUpdate(DocumentEvent+e)+{
++++changed();
++}
++public+void+insertUpdate(DocumentEvent+e)+{
++++changed();
++}

++public+void+changed()+{
+++++if+(yourJTextField.getText().equals("")){
+++++++loginButton.setEnabled(false);
+++++}
+++++else+{
+++++++loginButton.setEnabled(true);
++++}

++}
});|code-block|syntax|javascript|79816|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/3953208/value-change-listener-to-jtextfield^0|7|A|1C|G|1Y|H|2M|A|31|B|0|7|6|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]|$9|Z|A|10|B|C]|$9|11|A|12|B|C]|$9|13|A|14|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|15|8|@]|D|@$9|16|A|17|1|18]]|E|$]]|$1|H|3|I|5|J|7|19|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|1A|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]]]

For that you need to add change listener (a <code>DocumentListener</code> which reacts for change in the text) for your <code>JTextField</code>, and within <code>actionPerformed()</code>, you need to update the <code>loginButton</code> to enabled/disabled depending on the whether the <code>JTextfield</code> is empty or not. 

Below is what I found from this <a href="https://stackoverflow.com/questions/3953208/value-change-listener-to-jtextfield">thread</a>.

<pre><code>yourJTextField.getDocument().addDocumentListener(new DocumentListener() {
 public void changedUpdate(DocumentEvent e) {
 changed();
 }
 public void removeUpdate(DocumentEvent e) {
 changed();
 }
 public void insertUpdate(DocumentEvent e) {
 changed();
 }

 public void changed() {
 if (yourJTextField.getText().equals("")){
 loginButton.setEnabled(false);
 }
 else {
 loginButton.setEnabled(true);
 }

 }
});
</code></pre>

blocks|key|297092|text|好的，呈现按钮启用/禁用的代码：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|297093|if(name.getText().equals(""))+{
++++loginbt.setEnabled(false);
}else+{
++++loginbt.setEnabled(true);
}|code-block|syntax|javascript|297094|必须用javax.swing.event.ChangeListener编写并附加到字段中(请参阅here)。字段值的更改应触发侦听器重新评估对象状态。你还想要什么？|offset|length|style|CODE|297095|entityMap|0|LINK|mutability|MUTABLE|url|http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/6-b14/javax/swing/AbstractButton.java#AbstractButton.addChangeListener%2528javax.swing.event.ChangeListener%2529^0|0|0|3|W|1C|4|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|W|8|@$I|X|J|Y|K|L]]|9|@$I|Z|J|10|1|11]]|A|$]]|$1|M|3|-4|5|6|7|12|8|@]|9|@]|A|$]]]|N|$O|$5|P|Q|R|A|$S|T]]]]

Well, the code that renders the button enabled/disabled: 

<pre><code>if(name.getText().equals("")) {
 loginbt.setEnabled(false);
}else {
 loginbt.setEnabled(true);
}
</code></pre>

must be written in <code>javax.swing.event.ChangeListener</code> and attached to the field (see <a href="http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/6-b14/javax/swing/AbstractButton.java#AbstractButton.addChangeListener%28javax.swing.event.ChangeListener%29" rel="nofollow">here</a>). A change in field's value should trigger the listener to reevaluate the object state. What did you expect?

blocks|key|297105|text|您需要的是一种叫做文档侦听器的东西。参见How+to+Write+a+Document+Listener。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|297106|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.oracle.com/javase/tutorial/uiswing/events/documentlistener.html^0|K|W|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

What you need is something called Document Listener. See <a href="http://docs.oracle.com/javase/tutorial/uiswing/events/documentlistener.html" rel="nofollow">How to Write a Document Listener</a>.

blocks|key|297130|text|尝试在文本字段中使用keyListener|type|unstyled|depth|inlineStyleRanges|entityRanges|data|297131|jTextField.addKeyListener(new+KeyListener()+{

++++++++@Override
++++++++public+void+keyTyped(KeyEvent+e)+{
++++++++}

++++++++@Override
++++++++public+void+keyPressed(KeyEvent+e)+{
++++++++++++if+(text.getText().length()+>=+1)+{
++++++++++++++++button.setEnabled(true);
++++++++++++}+else+{
++++++++++++++++button.setEnabled(false);
++++++++++++}
++++++++}

++++++++@Override
++++++++public+void+keyReleased(KeyEvent+e)+{
++++++++}

++++});|code-block|syntax|javascript|297132|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Try with keyListener in your textfield

<pre><code>jTextField.addKeyListener(new KeyListener() {

 @Override
 public void keyTyped(KeyEvent e) {
 }

 @Override
 public void keyPressed(KeyEvent e) {
 if (text.getText().length() &gt;= 1) {
 button.setEnabled(true);
 } else {
 button.setEnabled(false);
 }
 }

 @Override
 public void keyReleased(KeyEvent e) {
 }

 });
</code></pre>

blocks|key|79883|text|尝尝这个|type|unstyled|depth|inlineStyleRanges|entityRanges|data|79884|if(name.getText()+!=+null+&&+name.getText().equals(""))
{
++++++++loginbt.setEnabled(false);
}
else
{
++++++++loginbt.setEnabled(true);
}|code-block|syntax|javascript|79885|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Try this

<pre><code>if(name.getText() != null &amp;&amp; name.getText().equals(""))
{
 loginbt.setEnabled(false);
}
else
{
 loginbt.setEnabled(true);
}
</code></pre>

blocks|key|79896|text|要检查JTextFiled是否为空，请执行以下操作：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|79897|if(+(billnotf.getText().length()==0)%7C%7C(billtabtf.getText().length()==0))|code-block|syntax|javascript|79898|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

To Check JTextFiled is empty or not condition:

<pre><code>if( (billnotf.getText().length()==0)||(billtabtf.getText().length()==0))
</code></pre>

blocks|key|297163|text|使用以下代码：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|297164|if(name.getText().equals(""))
{
loginbt.disable();
}|code-block|syntax|javascript|297165|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

use the following code :

<pre><code>if(name.getText().equals(""))
{
loginbt.disable();
}
</code></pre>

blocks|key|297199|text|如果JTextField+"name“不包含文本，则下面将返回true：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|297200|name.getText().isEmpty|offset|length|style|CODE|297201|entityMap^0|0|0|M|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|K|8|@$D|L|E|M|F|G]]|9|@]|A|$]]|$1|H|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|I|$]]

The following will return true if the JTextField "name" does not contain text:

<code>name.getText().isEmpty</code>

blocks|key|79995|text|if(name.getText().hashCode()+!=+0){
++++JOptionPane.showMessageDialog(null,+"not+empty");
}
else{
++++JOptionPane.showMessageDialog(null,+"empty");
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|79996|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>if(name.getText().hashCode() != 0){
 JOptionPane.showMessageDialog(null, "not empty");
}
else{
 JOptionPane.showMessageDialog(null, "empty");
}
</code></pre>

blocks|key|80011|text|private+void+jButton4ActionPerformed(java.awt.event.ActionEvent+evt)+{+++++++++++++++++++++++++++++++++++++++++
++++//+Submit+Button++++++++

++++String+Fname+=+jTextField1.getText();
++++String+Lname+=+jTextField2.getText();
++++String+Desig+=+jTextField3.getText();
++++String+Nic+=+jTextField4.getText();
++++String+Phone+=+jTextField5.getText();
++++String+Add+=+jTextArea1.getText();
++++String+Dob+=+jTextField6.getText();
++++//+String+Gender;
++++//+Image

++++if+(Fname.hashCode()+==+0+%7C%7C+Lname.hashCode()+==+0+%7C%7C+Desig.hashCode()+==+0+%7C%7C+Nic.hashCode()+==+0+%7C%7C+Phone.hashCode()+==+0+%7C%7C+Add.hashCode()+==+0)
++++{
++++++++JOptionPane.showMessageDialog(null,+"Some+fields+are+empty!");
++++}
++++else
++++{
++++++++JOptionPane.showMessageDialog(null,+"OK");
++++}
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|80012|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre class="lang-java prettyprint-override"><code>private void jButton4ActionPerformed(java.awt.event.ActionEvent evt) { 
 // Submit Button 

 String Fname = jTextField1.getText();
 String Lname = jTextField2.getText();
 String Desig = jTextField3.getText();
 String Nic = jTextField4.getText();
 String Phone = jTextField5.getText();
 String Add = jTextArea1.getText();
 String Dob = jTextField6.getText();
 // String Gender;
 // Image

 if (Fname.hashCode() == 0 || Lname.hashCode() == 0 || Desig.hashCode() == 0 || Nic.hashCode() == 0 || Phone.hashCode() == 0 || Add.hashCode() == 0)
 {
 JOptionPane.showMessageDialog(null, "Some fields are empty!");
 }
 else
 {
 JOptionPane.showMessageDialog(null, "OK");
 }
}
</code></pre>

So I got know this is a popular question and already found the solution. But when I try this it doesn't work properly.

My JTextField is empty and the button isn't enabled. When I write something in my textfield the button doesn't get enabled. 

So my program should check this field every second whether it's empty or not. As soon as someone writes something into the textfield the button should be enabled.^^

<pre><code>loginbt = new JButton("Login");
 loginbt.addActionListener(new loginHandler());
 add(loginbt);

 if(name.getText().equals("")) {
 loginbt.setEnabled(false);
 }else {
 loginbt.setEnabled(true);
 }
</code></pre>

Java - Check if JTextField is empty or not

所以我知道这是一个流行的问题，并且已经找到了解决方案。但是当我尝试这个的时候，它不能正常工作。我的JTextField为空，该按钮未启用。当我在我的文本字段中写一些东西的时候，按钮不会被激活。所以我的程序应该每秒检查一次这个字段，不管它是否为空。只要有人在文本字段中输入内容，就应该启用该按钮。^^loginbt = n...

问Java -检查JTextField是否为空
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