为什么在JtextField.setDocument()中设置的PlainDocument()会排除文本的一个字符

Question

有人知道为什么在JtextField中,当我设置setDocument()属性-class PlainDocument-当我执行程序时,它向我显示字段ok,但只有我可以输入N-1个字符,当我将maxlength prop设置为N字符长度.

// Block 1
txtPais.setDocument(new MaxLengthTextCntry());

我有另一个内部设置最大长度的类

// Block 2    
public class MaxLengthTextCntry extends MaxLengthGeneric{  
    public MaxLengthTextCntry(  
        {  
            super(2);  
        }  
    }

最后是MaxLengthGeneric类

// Block 3
public abstract class MaxLengthGeneric extends PlainDocument {

        private int maxChars;

        public MaxLengthGeneric(int limit) {
            super();
            this.maxChars = limit;
        }

        public void insertString(int offs, String str, AttributeSet a)
                throws BadLocationException {
            if (str != null && (getLength() + str.length() < maxChars)) {
                super.insertString(offs, str, a);
            }
        }
    }

解

维护块2,我用块1代替了块1

((AbstractDocument) txtRucnumero.getDocument()).setDocumentFilter(new MaxLengthTextRuc());

Block 3改变了DocumentFilter的依赖性.不要忘记实现父方法insertString()和replace()!!

public abstract class MaxLengthGeneric extends DocumentFilter {

...

    @Override
    public void insertString(FilterBypass fb, int offs, String str,
            AttributeSet a) throws BadLocationException {

        if ((fb.getDocument().getLength() + str.length()) <= maxChars)
            super.insertString(fb, offs, str, a);
        else
            Toolkit.getDefaultToolkit().beep();
    }

    @Override
    public void replace(FilterBypass fb, int offs, int length, String str,
            AttributeSet a) throws BadLocationException {
        if ((fb.getDocument().getLength() + str.length() - length) <= maxChars)
            super.replace(fb, offs, length, str, a);
        else
            Toolkit.getDefaultToolkit().beep();
    }
}

基于http://docs.oracle.com/javase/tutorial/uiswing/examples/components/TextComponentDemoProject/src/components/DocumentSizeFilter.java

或者解决方案2(或者可能是为Jnewbies生活调试的重要性:<replace with <=)

**    if (str != null && (getLength() + str.length() <= maxChars)) {**

Answer 1

MaxLengthTextArea是一个从PlainDocument扩展的类:用于通过参数设置我想要的字段数

正如我在评论中建议你应该使用的DocumentFilter.阅读有关实现文档过滤器的Swing教程中的部分以获取更多信息和工作示例.