问题描述

java菜鸟真心求教大神，谢谢！

请大神看看下面的代码，我检查了好几次都没发现错误，为何在编译的时候会出现java找不到符号的情况。。。。代码可能有点长。。。麻烦各位了，谢谢！

 //测试FileWriter类

public class TestFileWriter
{
    public static void showFile(java.io.File file)
    {
        char buff[] = new char[22];
        int ret = 0;

        System.out.println("Showfile begin["+file.getName()+"]:");

        java.io.FileReader read_file = null;

        try
        {
            //创建读取文件对象
            read_file = new java.io.FileReader(file);

            do
            {
                //读取一段字符，每次22个字符
                ret = read_file.read(buff);  

                for (int i=0; i<ret; i++)
                {
                    System.out.print(buff[i]);  //逐个输出读入的字符
                }
            }
            while (ret!=-1);
        }
        catch (java.lang.Exception e)
        {
            System.out.println("There must be something wrong!");
        }
        finally
        {
            //关闭打开的文件
            try
            {
                read_file.close();
            }
            catch (java.lang.Exception e)
            {
                System.out.println("Ignore the exception when closing.");
            }
        }

        System.out.println("nshowfile end ["+file.getName()+"].");
    }

    public static void main(String[] argv)
    {
        char buff[] = new char[48];
        char ch = 'A';
        int ret = 0;

        for (int i=0; i<26; i++)
        {
            buff[i] = ch++;  //输入A-Z共26个字母到字符数组buff
        }

        java.io.File _write = new java.io.File("_write.txt");
        java.io.FileWriter write_java = null;

        try
        {
            System.out.println(_write.getName()+"exist?"+_write.exists());

            write_java = new java.io.FileWriter("_write.txt");  //创建写入文本的对象

            System.out.println(_write.getName()+"exist?"+_write.exists());

            write_java.write(buff,0,26);  //将buff数组里的内容输出到指定文件

            System.out.println(_write.getName()+"exist?"+_write.exists());

            //write_java.flush();

            write_java.close();  //调用close（）会自动执行flush（），如果将这一行放在show_file（）方法后面，则show_file()显示文件为空，因为未写入

            System.out.println("nWrite into an empty file.");

            showFile(_write);  //调用show_file()方法
        }
        catch (java.lang.Exception e)
        {
            System.out.println("There must be something wrong!");
        }
        finally
        {
            try
            {
                write_java.close();
            }
            catch (java.lang.Exception e)
            {
                System.out.println("Ignore the exception when closing.");
            }

            java.io.FileWriter append_java = null; 

        }

        try
        {
            //使用append（）方法向文件追加内容
            append_java = new java.io.FileWriter(_write);  //以普通形式打开，结果依然覆盖原文
            append_java.append("Someting appended in the file....");
            append_java.close();

            System.out.println("n以普通方式打开，调用append()方法");
            showFile(_write);
        }
        catch (java.lang.Exception e)
        {
            System.out.println("There must be something wrong!");
        }
        finally
        {
            try
            {
                append_java.close();
            }
            catch (java.lang.Exception e)
            {
                System.out.println("Ignore the exception when closing.");
            }
        }

        try
        {
            //以追加方式打开文件，并使用append（）方法向文件追加内容

            append_java = new java.io.FileWriter(_write, true);
            append_java.write(buff,0,26);
            append_java.close();

            System.out.println("n以追加模式打开文件，用append（）方法追加内容到文件中");
            showFile(_write);
        }
        catch (java.lang.Exception e)
        {
            System.out.println("There must be something wrong!");
        }
        finally
        {
            try
            {
                append_java.close();
            }
            catch (java.lang.Exception e)
            {
                System.out.println("Ignore the exception when closing.");
            }
        }

        try
        {
            //以非追加方式打开，并用append（）方法向文件追加内容
            append_java = new java.io.FileWriter(_write, false);
            append_java.append(new String(buff).trim());
            append_java.close();
            System.out.println("n以非追加方式打开，调用append（）方法");
            showFile(_write);
        }
        catch (java.lang.Exception e)
        {
            System.out.println("There must be something wrong!");
        }
        finally
        {
            try
            {
                append_java.close();
            }
            catch (java.lang.Exception e)
            {
                System.out.println("Ignore the exception when closing.");
            }
        }

        _write.delete();
    }
}

解决方案

 finally
        {
            try
            {
                write_java.close();
            }
            catch (java.lang.Exception e)
            {
                System.out.println("Ignore the exception when closing.");
            }

            java.io.FileWriter append_java = null; 

        }

        try
        {
            //使用append（）方法向文件追加内容
            append_java = new java.io.FileWriter(_write);  //以普通形式打开，结果依然覆盖原文
            append_java.append("Someting appended in the file....");
            append_java.close();

            System.out.println("n以普通方式打开，调用append()方法");
            showFile(_write);
        }
                改成
                finally
        {
            try
            {
                write_java.close();
            }
            catch (java.lang.Exception e)
            {
                System.out.println("Ignore the exception when closing.");
            }

        }

            java.io.FileWriter append_java = null; //把这个变量申明拿出来
        try
        {
            //使用append（）方法向文件追加内容
            append_java = new java.io.FileWriter(_write);  //以普通形式打开，结果依然覆盖原文
            append_java.append("Someting appended in the file....");
            append_java.close();

            System.out.println("n以普通方式打开，调用append()方法");
            showFile(_write);
        }

解决方案二：

另外下次提问的时候可以把错误信息也一起贴出来

解决方案三：

这些问题只要在IDE编译器里都会很快解决的，我放到我的Eclipse里面直接就提示了，你的append_java没有声明对象，声明一下就可以了。看代码：

public class TestFileWriter {
    public static void showFile(java.io.File file) {
        char buff[] = new char[22];
        int ret = 0;

        System.out.println("Showfile begin[" + file.getName() + "]:");

        java.io.FileReader read_file = null;

        try {
            // 创建读取文件对象
            read_file = new java.io.FileReader(file);

            do {
                // 读取一段字符，每次22个字符
                ret = read_file.read(buff);

                for (int i = 0; i < ret; i++) {
                    System.out.print(buff[i]); // 逐个输出读入的字符
                }
            } while (ret != -1);
        } catch (java.lang.Exception e) {
            System.out.println("There must be something wrong!");
        } finally {
            // 关闭打开的文件
            try {
                read_file.close();
            } catch (java.lang.Exception e) {
                System.out.println("Ignore the exception when closing.");
            }
        }

        System.out.println("nshowfile end [" + file.getName() + "].");
    }

    public static void main(String[] argv) {
        char buff[] = new char[48];
        char ch = 'A';
        int ret = 0;

        for (int i = 0; i < 26; i++) {
            buff[i] = ch++; // 输入A-Z共26个字母到字符数组buff
        }

        java.io.File _write = new java.io.File("_write.txt");
        java.io.FileWriter write_java = null;

        try {
            System.out.println(_write.getName() + "exist?" + _write.exists());

            write_java = new java.io.FileWriter("_write.txt"); // 创建写入文本的对象

            System.out.println(_write.getName() + "exist?" + _write.exists());

            write_java.write(buff, 0, 26); // 将buff数组里的内容输出到指定文件

            System.out.println(_write.getName() + "exist?" + _write.exists());

            // write_java.flush();

            write_java.close(); // 调用close（）会自动执行flush（），如果将这一行放在show_file（）方法后面，则show_file()显示文件为空，因为未写入

            System.out.println("nWrite into an empty file.");

            showFile(_write); // 调用show_file()方法
        } catch (java.lang.Exception e) {
            System.out.println("There must be something wrong!");
        } finally {
            try {
                write_java.close();
            } catch (java.lang.Exception e) {
                System.out.println("Ignore the exception when closing.");
            }

            java.io.FileWriter append_java = null;

        }

        FileWriter append_java = null;
        try {
            // 使用append（）方法向文件追加内容
            append_java = new java.io.FileWriter(_write); // 以普通形式打开，结果依然覆盖原文
            append_java.append("Someting appended in the file....");
            append_java.close();

            System.out.println("n以普通方式打开，调用append()方法");
            showFile(_write);
        } catch (java.lang.Exception e) {
            System.out.println("There must be something wrong!");
        } finally {
            try {
                append_java.close();
            } catch (java.lang.Exception e) {
                System.out.println("Ignore the exception when closing.");
            }
        }

        try {
            // 以追加方式打开文件，并使用append（）方法向文件追加内容

            append_java = new java.io.FileWriter(_write, true);
            append_java.write(buff, 0, 26);
            append_java.close();

            System.out.println("n以追加模式打开文件，用append（）方法追加内容到文件中");
            showFile(_write);
        } catch (java.lang.Exception e) {
            System.out.println("There must be something wrong!");
        } finally {
            try {
                append_java.close();
            } catch (java.lang.Exception e) {
                System.out.println("Ignore the exception when closing.");
            }
        }

        try {
            // 以非追加方式打开，并用append（）方法向文件追加内容
            append_java = new java.io.FileWriter(_write, false);
            append_java.append(new String(buff).trim());
            append_java.close();
            System.out.println("n以非追加方式打开，调用append（）方法");
            showFile(_write);
        } catch (java.lang.Exception e) {
            System.out.println("There must be something wrong!");
        } finally {
            try {
                append_java.close();
            } catch (java.lang.Exception e) {
                System.out.println("Ignore the exception when closing.");
            }
        }

        _write.delete();
    }
}

解决方案四：

append _java 变量申明的地方错了，放到finally语句块以外就可以了

解决方案五：

恩，我是照着书本打的，刚开始我也觉得疑惑，为啥声明一个对象会放在finally里面。。。自己也试过把它拿出来另起一行，可能当时也没写对位置吧，总之谢谢啦