Java知识点-week2（枚举，继承）

枚举类

将普通的Java类的calss替换为enum，创建属性值时不需要添加;

例：

public enum Animal {
    tiger,
    lion,
    dog,
    cat
}

继承

public class Apple extends Fruit{

}

父类转换成子类，需要强制转换。

子类转换成父类，直接=符号赋值。

文件读写

文件读取

public static void read(){
    File file = new File("E:\\临时.txt");
    BufferedReader br = null;
    try {
        br = new BufferedReader(new FileReader(file));
        String line;
        while ((line = br.readLine()) != null){
            System.out.println(line);
        }
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        if( br != null){
            try {
                br.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

BufferedReader是比FileReader更为简洁的代码编写，主要体现在缓存区中，BufferedReader读取时将字符串一行一行的读取。

文件写入

public static void write(){
    File file = new File("E:\\临时.txt");
    BufferedWriter bw = null;
    try {
        bw = new BufferedWriter(new FileWriter(file));
        bw.write("hello bmatch");
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        if(bw != null){
            try {
                bw.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

Excel文件读写

Excel文件读取

public static void read(){
    InputStream inputStream = null;
    try {
        inputStream = new FileInputStream("E:\\test\\workbook.xlsx");
        Workbook wb = WorkbookFactory.create(inputStream);
        DataFormatter formatter = new DataFormatter();
        Sheet sheet1 = wb.getSheetAt(0);
        for (Row row : sheet1) {
            for (Cell cell : row) {
                CellReference cellRef = new CellReference(row.getRowNum(), cell.getColumnIndex());
                System.out.print(cellRef.formatAsString());
                System.out.print(" - ");

                // get the text that appears in the cell by getting the cell value and applying any data formats (Date, 0.00, 1.23e9, $1.23, etc)
                String text = formatter.formatCellValue(cell);
                System.out.println(text);

                // Alternatively, get the value and format it yourself
                switch (cell.getCellType()) {
                    case STRING:
                        System.out.println(cell.getRichStringCellValue().getString());
                        break;
                    case NUMERIC:
                        if (DateUtil.isCellDateFormatted(cell)) {
                            System.out.println(cell.getDateCellValue());
                        } else {
                            System.out.println(cell.getNumericCellValue());
                        }
                        break;
                    case BOOLEAN:
                        System.out.println(cell.getBooleanCellValue());
                        break;
                    case FORMULA:
                        System.out.println(cell.getCellFormula());
                        break;
                    case BLANK:
                        System.out.println();
                        break;
                    default:
                        System.out.println();
                }
            }
        }

    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        if(inputStream != null){
            try {
                inputStream.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

}

Excel文件写入

public static void write(){
    Workbook wb = null;
    OutputStream fileOut = null;
    try {
        fileOut = new FileOutputStream("E:\\test\\workbook.xlsx");
        wb = new XSSFWorkbook();
        Sheet sheet = wb.createSheet("new sheet");
        Row row = sheet.createRow(0);
        Cell cell0 = row.createCell(0);
        cell0.setCellValue(1.0);

        Cell cell1 = row.createCell(1);
        cell1.setCellValue("hello bmatch");

        CreationHelper createHelper = wb.getCreationHelper();
        CellStyle cellStyle = wb.createCellStyle();
        cellStyle.setDataFormat(
                createHelper.createDataFormat().getFormat("m/d/yy h:mm"));

        Cell cell2 = row.createCell(2);
        cell2.setCellValue(new Date());
        cell2.setCellStyle(cellStyle);
        wb.write(fileOut);
    }  catch (IOException e) {
        e.printStackTrace();
    } finally {
        if (fileOut != null) {
            try {
                fileOut.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}