blocks|key|1422777|text|在使用JDK1.4.2+(或更早版本)时，论坛中最常见的建议是使用如下代码：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1422778|textArea.append(...);
textArea.setCaretPosition(textArea.getDocument().getLength());|code-block|syntax|javascript|1422779|然而，我刚刚注意到，在JDK5中，这个问题实际上已经通过一个API更改得到了解决。现在，您可以通过在文本区域的DefaultCaret上设置一个属性来控制此行为。使用这种方法，代码将是：|1422780|JTextArea+textArea+=+new+JTextArea();
DefaultCaret+caret+=+(DefaultCaret)textArea.getCaret();
caret.setUpdatePolicy(DefaultCaret.ALWAYS_UPDATE);|1422781|注意：|1422782|上述设置插入符号更新策略的建议不起作用。|1422783|相反，您可能想要查看Smart+Scrolling，它使用户能够确定何时应该自动滚动。|offset|length|1422784|有关文本区域中自动滚动的更详细说明，可在此处找到：Text+Area+Scrolling|1422785|entityMap|0|LINK|mutability|MUTABLE|url|https://tips4java.wordpress.com/2013/03/03/smart-scrolling/|1|https://tips4java.wordpress.com/2008/10/22/text-area-scrolling/^0|0|0|0|0|0|0|A|F|0|0|P|J|1|0^^$0|@$1|2|3|4|5|6|7|14|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|15|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|16|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|17|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|18|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|19|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|1A|8|@]|9|@$Q|1B|R|1C|1|1D]]|A|$]]|$1|S|3|T|5|6|7|1E|8|@]|9|@$Q|1F|R|1G|1|1H]]|A|$]]|$1|U|3|-4|5|6|7|1I|8|@]|9|@]|A|$]]]|V|$W|$5|X|Y|Z|A|$10|11]]|12|$5|X|Y|Z|A|$10|13]]]]

When using JDK1.4.2 (or earlier) the most common suggestion you will find in the forums is to use code like the following:

<pre><code>textArea.append(...);
textArea.setCaretPosition(textArea.getDocument().getLength());
</code></pre>

However, I have just noticed that in JDK5 this issue has actually been resolved by an API change. You can now control this behaviour by setting a property on the DefaultCaret of the text area. Using this approach the code would be:

<pre><code>JTextArea textArea = new JTextArea();
DefaultCaret caret = (DefaultCaret)textArea.getCaret();
caret.setUpdatePolicy(DefaultCaret.ALWAYS_UPDATE);
</code></pre>

<h3>Note:</h3>

The above suggestion to set the caret update policy does not work. 

Instead you may want to check out <a href="https://tips4java.wordpress.com/2013/03/03/smart-scrolling/" rel="noreferrer">Smart Scrolling</a> which gives the user the ability to determine when scrolling should be automatic or not.

A more detailed description of automatic scrolling in a text area can be found here: <a href="https://tips4java.wordpress.com/2008/10/22/text-area-scrolling/" rel="noreferrer">Text Area Scrolling</a>

blocks|key|1422794|text|++++JScrollBar+vbar+=+scrollPane.getVerticalScrollBar();

++++for+(int+i+=+0;+i+<+20;+i%2B%2B)+{

++++++++myJTxt.append("This+is+text+"+%2B+i+%2B+"\n");
++++++++vbar.setValue(vbar.getMaximum());
++++++++vbar.paint(vbar.getGraphics());
++++++++myJTxt.scrollRectToVisible(myJTxt.getVisibleRect());
++++++++myJTxt.paint(myJTxt.getGraphics());
++++++++try+{
++++++++++++Thread.sleep(250);
++++++++}+catch+(InterruptedException+ex)+{
++++++++++++Logger.getLogger(ScrollTextView.class.getName()).log(Level.SEVERE,+null,+ex);
++++++++}
++++}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1422795|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> JScrollBar vbar = scrollPane.getVerticalScrollBar();

 for (int i = 0; i &lt; 20; i++) {

 myJTxt.append("This is text " + i + "\n");
 vbar.setValue(vbar.getMaximum());
 vbar.paint(vbar.getGraphics());
 myJTxt.scrollRectToVisible(myJTxt.getVisibleRect());
 myJTxt.paint(myJTxt.getGraphics());
 try {
 Thread.sleep(250);
 } catch (InterruptedException ex) {
 Logger.getLogger(ScrollTextView.class.getName()).log(Level.SEVERE, null, ex);
 }
 }
</code></pre>

blocks|key|1422806|text|试试这个：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1422807|JTextArea+jTextArea+=+new+JTextArea();
JScrollPane+jScrollPane+=+new+JScrollPane();
jScrollPane.setViewport(jTextArea);|code-block|syntax|javascript|1422808|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>JTextArea jTextArea = new JTextArea();
JScrollPane jScrollPane = new JScrollPane();
jScrollPane.setViewport(jTextArea);
</code></pre>

blocks|key|1422869|text|当您在JTextArea上的任意位置单击时，可能会停止自动滚动。因为插入符号的位置改变了一次，视点也改变了。此时，您应该在追加或添加一些文本时设置插入符号位置。在我的方法中，我创建了包括设置插入符号位置的方法，然后在添加或附加任何内容时使用它。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1422870|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

When you click anywhere over JTextArea, auto-scrolling have possible to be stopped. Because the position of caret once changed, view point changed too. In this time you should set caret position when you append or add some text. On my way, I made method including set caret position, and then use it when anything to be added or appended.

blocks|key|1207819|text|++++JTextArea+jTextArea+=+new+JTextArea();
++++DefaultCaret+caret+=+(DefaultCaret)jTextArea.getCaret();
++++caret.setUpdatePolicy(DefaultCaret.OUT_BOTTOM);|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1207820|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> JTextArea jTextArea = new JTextArea();
 DefaultCaret caret = (DefaultCaret)jTextArea.getCaret();
 caret.setUpdatePolicy(DefaultCaret.OUT_BOTTOM);
</code></pre>

blocks|key|1207828|text|改用这个|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1207829|JTextArea+textArea+=+new+JTextArea();
DefaultCaret+caret+=+(DefaultCaret)textArea.getCaret();
caret.setUpdatePolicy(DefaultCaret.ALWAYS_UPDATE);
scrollPane+=+new+JScrollPane();
scrollPane.add(textArea);
scrollPane.setViewportView(textArea);|code-block|syntax|javascript|1207830|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 this instead

<pre><code>JTextArea textArea = new JTextArea();
DefaultCaret caret = (DefaultCaret)textArea.getCaret();
caret.setUpdatePolicy(DefaultCaret.ALWAYS_UPDATE);
scrollPane = new JScrollPane();
scrollPane.add(textArea);
scrollPane.setViewportView(textArea);
</code></pre>

blocks|key|1207921|text|我尝试了大多数建议，但当JTextArea的内容变得很大(几MB)时遇到了问题。最后，下面显示了最佳性能：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1207922|myTextArea.append(+someText+);
myTextArea.getCaret().setDot(+Integer.MAX_VALUE+);|code-block|syntax|javascript|1207923|当然，用户所做的任何选择都会丢失。因此，它只适用于“仅显示”的文本区。|1207924|尽管如此，在我的安装中，如果JTextArea的内容超过9MB，它就会变得无法使用(非常慢，几乎冻结了图形用户界面)。|1207925|当文本包含由UTF-16编码中的两个字符(两个16位单元)表示的字符(即所谓的代理对，如下所示)时，也会出现类似的现象。我有一个过滤的解决方案，但可能是一个不同的主题。|1207926|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

I tried most suggestions but ran into problems when the content of the JTextArea becomes large (several MB). Finally the following showed best performance:

<pre><code>myTextArea.append( someText );
myTextArea.getCaret().setDot( Integer.MAX_VALUE );
</code></pre>

Of course, any selection the user had made gets lost. Hence, its only usable for a "display-only" usage of the text area.

Still, in my installation, if the content of the JTextArea exceeds some 9MB, it gets kind of unusable (very sluggish to almost frozen GUI).

A similar phenomenon occurs when the text contains characters that are represented by two chars (two 16-bit units) in the UTF-16 encoding (so-called surrogate pairs, like this: ). I have a solution for filtering, but maybe a different topic.

blocks|key|1207968|text|最好也是最简单的方法，试试这个：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1207969|++import+javax.swing.text.DefaultCaret;
++DefaultCaret+caret+=+(DefaultCaret)+textArea.getCaret();
++caret.setUpdatePolicy(DefaultCaret.ALWAYS_UPDATE);|code-block|syntax|javascript|1207970|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|$]]

Best and easiest way, Try this :
<pre><code> import javax.swing.text.DefaultCaret;
 DefaultCaret caret = (DefaultCaret) textArea.getCaret();
 caret.setUpdatePolicy(DefaultCaret.ALWAYS_UPDATE);
</code></pre>

I have embedded a JTextArea on a JScrollPane and am using that JTextArea for output.

I want that whenever the ouput goes beyond the size of the JTextArea, the JTextArea scrolls automatically so that user don't have to do manual scroll down to see the recent output.

How can I do that?

I have already set the autoscroll property of both JTextArea and JScrollPane to true.

How to set AUTO-SCROLLING of JTextArea in Java GUI?

我已经在JScrollPane上嵌入了一个JTextArea，并且正在使用该JTextArea进行输出。我希望只要输出超过JTextArea的大小，JTextArea就会自动滚动，这样用户就不必手动向下滚动来查看最近的输出。我该怎么做呢？我已经将JTextArea和JScrollPane的自动滚动属性都设置为true。

问如何在Java GUI中设置JTextArea的自动滚动？
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