一周Java开发问题记录

当remove 导入的jar包后，在jar文件上右键会没有build path选项

直接在项目包文件夹上右键–>配置build path、

一个JFrame中加入多个JButton时，最后一个JButton会存在现实异常

可以加一个空的JButton，不使用

将double或者float型数值转换为字符串

float dec = 0.12345f;

//读取文件
DecimalFormat df = new DecimalFormat("#%");//乘以100后以百分比形式输出,此处输出"12%"
DecimalFormat df = new DecimalFormat("##.##");//输出"0.12"
DecimalFormat df = new DecimalFormat("00.00");//输出"00.12"
String s = df.format(dec);
System.out.println(s);

Java读取文件对话框，并读取.xlsx格式文件(输出)

Student student = null;
List<String> array = new ArrayList<>();
fd = new FileDialog(f, "Open", FileDialog.LOAD);
fd.setVisible(true);

try

{
file1 = new File(fd.getDirectory(), fd.getFile());
InputStream instream = new FileInputStream(file1);

xssfWorkbook = new XSSFWorkbook(instream);

XSSFSheet xssfSheet = xssfWorkbook.getSheetAt(0);

for (int rowNum = 1; rowNum <= xssfSheet.getLastRowNum(); rowNum++) {
xssfRow = xssfSheet.getRow(rowNum);
student = new Student();
xssfRow.getCell(0).setCellType(Cell.CELL_TYPE_STRING);
xssfRow.getCell(1).setCellType(Cell.CELL_TYPE_STRING);
xssfRow.getCell(2).setCellType(Cell.CELL_TYPE_STRING);
xssfRow.getCell(3).setCellType(Cell.CELL_TYPE_STRING);
xssfRow.getCell(4).setCellType(Cell.CELL_TYPE_STRING);

student.setStudentId(xssfRow.getCell(0).getStringCellValue());
student.setStudentName(xssfRow.getCell(1).getStringCellValue());
student.setStudentPic(xssfRow.getCell(2).getStringCellValue());
student.setCalledNumber(Integer.valueOf(xssfRow.getCell(3).getStringCellValue()));
student.setLateNumber(Integer.valueOf(xssfRow.getCell(4).getStringCellValue()));

pList.add(student);

}
instream.close();
flushWindow(pList);
} catch (IOException ioe) {
ioe.printStackTrace();
}

//输出文件
try {
file2 = new File("学期报表.xlsx");
OutputStream outstream = new FileOutputStream(file2);

xssfWorkbook = new XSSFWorkbook();
XSSFSheet xssfSheet = xssfWorkbook.createSheet();

XSSFRow xssfRow = xssfSheet.createRow(0);
xssfRow.createCell(0).setCellValue("学号");
xssfRow.createCell(1).setCellValue("姓名");
xssfRow.createCell(2).setCellValue("图片地址");
xssfRow.createCell(3).setCellValue("被叫次数");
xssfRow.createCell(4).setCellValue("迟到次数");
xssfRow.createCell(5).setCellValue("总评成绩");

for (int rowNum = 0; rowNum < pList.size(); rowNum++) {
xssfRow = xssfSheet.createRow(rowNum + 1);
xssfRow.createCell(0).setCellValue(pList.get(rowNum).getStudentId());
xssfRow.createCell(1).setCellValue(pList.get(rowNum).getStudentName());
xssfRow.createCell(2).setCellValue(pList.get(rowNum).getStudentPic());
xssfRow.createCell(3).setCellValue(String.valueOf(pList.get(rowNum).getCalledNumber()));
xssfRow.createCell(4).setCellValue(String.valueOf(pList.get(rowNum).getLateNumber()));
if (pList.get(rowNum).getCalledNumber() == 0) {
xssfRow.createCell(5).setCellValue("0");
} else {
double result = (double) pList.get(rowNum).getLateNumber()
/ pList.get(rowNum).getCalledNumber();
DecimalFormat df = new DecimalFormat("#%");// 乘以100后以百分比形式输出,此处输出"12%"
String str = df.format(result);
xssfRow.createCell(5).setCellValue(str);
}

xssfRow.getCell(0).setCellType(Cell.CELL_TYPE_STRING);
xssfRow.getCell(1).setCellType(Cell.CELL_TYPE_STRING);
xssfRow.getCell(2).setCellType(Cell.CELL_TYPE_STRING);
xssfRow.getCell(3).setCellType(Cell.CELL_TYPE_STRING);
xssfRow.getCell(4).setCellType(Cell.CELL_TYPE_STRING);
xssfRow.getCell(5).setCellType(Cell.CELL_TYPE_STRING);
}
xssfWorkbook.write(outstream);
outstream.flush();
outstream.close();
PublicWindowSet.promptPopUp("输出报表文件成功!!!", "提示", frame);
} catch (IOException ioe) {
ioe.printStackTrace();
}

项目检出JRE问题(Unbound classpath container: ‘JRE System Library [JavaSE-1.7]’ in project ‘idweb’)

Uncaught error fetching image

jdk版本不对应，可能过低

Operation not allowed after ResultSet closed的问题

数据库执行操作未关闭

java乱码的几个地方修改

windows - preferences - general - content types

windows - preferences - general - workspace

项目右键 - preferences

文件右键 - preferences

项目右键 - run configure - common