使用if条件如何提高代码标准？

Question

假设我想在迭代列表时检查特定条件，我使用了很多违反编码标准的 if 条件。我有以下带有许多 if 条件的代码，如何在不改变输出的情况下减少编码行数并提高代码质量。

请在使用 if 条件时建议我一些好的标准。

while (iterator.hasNext()) {
            Row nextRow = iterator.next();
            for (int colIndex = 0; colIndex < 7; colIndex++) {
                if (colIndex == 0) {
                      Cell cell = nextRow.getCell(colIndex);
                      if (cell != null) {
                          firstName = cell.getStringCellValue();
                          System.out.println("First Name : "+firstName);
                      }
                  }
                if (colIndex == 1) {
                    Cell cell = nextRow.getCell(colIndex);
                    if (cell != null) {
                        middleName = cell.getStringCellValue();
                        System.out.println("Middle Name : "+middleName);
                    }
                }
                if (colIndex == 2) {
                    Cell cell = nextRow.getCell(colIndex);
                    if (cell != null) {
                        lastName = cell.getStringCellValue();
                        System.out.println("Last Name : "+lastName);
                    }
                }
                if (colIndex == 3) {
                    Cell cell = nextRow.getCell(colIndex);
                    if (cell != null) {
                        email = cell.getStringCellValue();
                        System.out.println("Email : "+email);
                    }
                }
                if (colIndex == 4) {
                    Cell cell = nextRow.getCell(colIndex);
                    if (cell != null) {
                        password = cell.getStringCellValue();
                        System.out.println("Password : "+password);
                    }
                }
                if (colIndex == 5) {
                    Cell cell = nextRow.getCell(colIndex);
                    if (cell != null) {
                        role = cell.getStringCellValue();
                        System.out.println("Role : "+role);
                    }
                }
                if (colIndex == 6) {
                    Cell cell = nextRow.getCell(colIndex);
                    if (cell != null) {
                        status = cell.getStringCellValue();
                        System.out.println("Status : "+status);
                    }
                }
            }
            System.out.println();
        }

Answer 1

首先将if移到switch。然后你可以减少每个条件下的前两行只写一次

 for (int colIndex = 0; colIndex < 7; colIndex++) {
 Cell cell = nextRow.getCell(colIndex);
 if (cell != null) {
  value= cell.getStringCellValue();
  switch (intParam) {
     case 1:
     System.out.println("First Name : "+firstName);
     break;
     case 2 : 
     // and so on.. 
  }
 }

注意：手头没有IDE，如有编译时错误请解决。

Answer 2

使用 switch statement 作为 if，如下所示。当您在最坏的情况下使用 switch 时，编译器将生成与 if-else 链相同的代码。其他时候它会提供比 if-else 更好的性能。最好将最常见的情况 1st 用于 switch 语句。

while (iterator.hasNext()) {
    Row nextRow = iterator.next();
    for (int colIndex = 0; colIndex < 7; colIndex++) {

    switch(colIndex){
        case 0 :
              Cell cell = nextRow.getCell(colIndex);
              if (cell != null) {
                  firstName = cell.getStringCellValue();
                  System.out.println("First Name : "+firstName);
              }
        break;  
        case 1 :
            Cell cell = nextRow.getCell(colIndex);
            if (cell != null) {
                middleName = cell.getStringCellValue();
                System.out.println("Middle Name : "+middleName);
            }
            break;
        case 2 :
            Cell cell = nextRow.getCell(colIndex);
            if (cell != null) {
                lastName = cell.getStringCellValue();
                System.out.println("Last Name : "+lastName);
            }
            break;
        case 3 :
            Cell cell = nextRow.getCell(colIndex);
            if (cell != null) {
                email = cell.getStringCellValue();
                System.out.println("Email : "+email);
            }
            break;
        case 4 :
            Cell cell = nextRow.getCell(colIndex);
            if (cell != null) {
                password = cell.getStringCellValue();
                System.out.println("Password : "+password);
            }
            break;
        case 5 :
            Cell cell = nextRow.getCell(colIndex);
            if (cell != null) {
                role = cell.getStringCellValue();
                System.out.println("Role : "+role);
            }
            break;
        case 6 :
            Cell cell = nextRow.getCell(colIndex);
            if (cell != null) {
                status = cell.getStringCellValue();
                System.out.println("Status : "+status);
            }
        break;
        }
    }
    System.out.println();
}

Answer 3

大部分代码在每个分支中保持不变：

Cell cell = nextRow.getCell(colIndex);
String value = null;
if (cell != null) {
    value = cell.getStringCellValue(); // the name of the variable differs here, but it's always a string?

...因此您可以在 if 块之前执行此操作。如果它不总是一个字符串，您至少可以在 if 之前获取单元格。然后你可以使用开关盒...

switch(colIndex) {
    case 1: firstName = value; break;
//etc.

如果分支很复杂，您可能会考虑使用枚举。

enum CellValue {

    FIRST_NAME(0) {
        public void doSomething(Cell cell) {
            ...do something.
        }
     },

     // etc.

     private final int colIndex;

     private CellValue(int colIndex) {
         this.colIndex = colIndex;
     }

    public abstract void doSomething(Cell cell);

    public static void work(int colIndex, Something nextRow) {
        for(CellValue value : values()) {
            if (value.colIndex == colIndex) {
                value.work(newRow.getCell(colIndex));
                return;  
            }
        }
        // throw exception here
    }
}

这样，您就可以简单地调用...

CellValue.work( colIndex, nextRow );

Answer 4

你有一个绝好的机会 enum:

enum Field {

    FirstName,
    MiddleName,
    LastName,
    EMail,
    Password,
    Role,
    Status;
}

public void test() {
    while (iterator.hasNext()) {
        Row nextRow = iterator.next();
        Map<Field, String> values = new EnumMap(Field.class);
        for (Field f : Field.values()) {
            Cell cell = nextRow.getCell(f.ordinal());
            if (cell != null) {
                values.put(f, cell.getStringCellValue());
            }
        }
    }
}

Answer 5

取决于您的列的固定程度。由于您目前使用 for 循环并没有从中获益太多，因此您甚至可以直接存储数据。

...
while (iterator.hasNext()) {
  Row next = iterator.next();
  firstName = saveGetCell(firstName, 0, next);
  middleName = saveGetCell(middleName, 1, next);
  lastName = saveGetCell(lastName, 2, next);
  email = saveGetCell(email, 3, next);
  password = saveGetCell(password, 4, next);
  role = saveGetCell(role, 5, next);
  status = saveGetCell(status, 6, next);
}

private String saveGetCell(String saveValue, int index, Row row) {
  Cell cell = row.getCell(index);
  String result = null;
  if(cell != null) {
    result = cell.getStringCellValue();
  }
  return result == null ? saveValue : result;
}

Answer 6

private void CycleFunc()
{
    while (iterator.hasNext()) {
            Row nextRow = iterator.next();
            for (int colIndex = 0; colIndex < 7; colIndex++) 
            {
                String result = GetCellStatus(colIndex);
                System.out.println(result); 
            }
            System.out.println();
        }
}

private string GetCellStatus(int colIndex)
{
    String result;
    switch(colIndex)
    {
    case:0: 
        result = "Middle Name : "+GetStingFromCell(colIndex);
        break;
    case:1: 
        result = "Last Name : "+GetStingFromCell(colIndex);
        break;
    case:2: 
        result = "Email : "+GetStingFromCell(colIndex);
        break;
    case:3: 
        result = "Password: "+GetStingFromCell(colIndex);
        break;
    case: 4: 
        result = "Role : "+GetStingFromCell(colIndex);
        break;
    case:5: 
        result = "Status : "+GetStingFromCell(colIndex);
        break;
    case:6: 
        result = "Middle Name : "+GetStingFromCell(colIndex);
        break;
    default: 
        result = "Some error";
        break;
    }
    return result;
}

private string GetStingFromCell(int colIndex)
{
    String str;
    Cell cell = nextRow.getCell(colIndex);
                      if (cell != null) {
                          str = cell.getStringCellValue();
                      }
    return str;
}

使用if条件如何提高代码标准？

How to improve the code standards while using if conditions?

java

for-loop

if-statement

switch-statement