每个软件组件都应该只有一个且一个职责

软件组件可以是类、方法或模块

例如，瑞士军刀是一种多用途工具，违反了软件开发的单一责任原则，相反，刀是遵循单一责任的一个很好的例子（因为它只能用于切割，而瑞士军刀可以用于切割、打开罐头、作为万能钥匙、剪刀等）

由于无论是在现实世界还是在软件开发中，变化都是不断变化的，单一职责原则的定义也会随之变化

每个软件组件都应该有一个且仅有一个更改的理由

下面的 employee 类会发生变化的原因有以下三个

员工属性变化
数据库更改
税收计算方式的变化

import java.sql.connection;
import java.sql.drivermanager;
import java.sql.statement;

/**

• employee class has details of employee
• this class is responsible for saving employee details, getting tax of
• employee and getting

• details of employee like name, id, address, contact, etc.
  */
  public class employee {
  private string employeeid;
  private string employeename;
  private string employeeaddress;
  private string contactnumber;
  private string employeetype;

  public void save() {
  string insert = myutil.serializeintostring(this);
  connection connection = null;
  statement statement = null;
  try {
  class.forname("com.mysql.jdbc.driver");
  connection = drivermanager.getconnection("jdbc://mysql://localhost:8080/mydb", "root", "password");
  statement = connection.createstatement();
  statement.execute("insert into employee values (" + insert + ")");

  } catch (exception e) {
      e.printstacktrace();
  }

  }

  public void calculatetax() {
  if (this.getemployeetype().equals("fulltime")) {
  // tax calculation for full time employee
  } else if (this.getemployeetype().equals("contract")) {
  // tax calculation for contract type employee
  }
  }

  public string getemployeeid() {
  return employeeid;
  }

  public void setemployeeid(string employeeid) {
  this.employeeid = employeeid;
  }

  public string getemployeename() {
  return employeename;
  }

  public void setemployeename(string employeename) {
  this.employeename = employeename;
  }

  public string getemployeeaddress() {
  return employeeaddress;
  }

  public void setemployeeaddress(string employeeaddress) {
  this.employeeaddress = employeeaddress;
  }

  public string getcontactnumber() {
  return contactnumber;
  }

  public void setcontactnumber(string contactnumber) {
  this.contactnumber = contactnumber;
  }

  public string getemployeetype() {
  return employeetype;
  }

  public void setemployeetype(string employeetype) {
  this.employeetype = employeetype;
  }

}
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由于srp（单一职责原则）建议在类中只有一个更改原因，因此我们必须在employee类中进行一些修改

srp 的更改

现在，employee 类中发生变化的原因只有一个

变更原因：员工属性变更

/**

• employee class has details of employee
  */
  public class employee {
  private string employeeid;
  private string employeename;
  private string employeeaddress;
  private string contactnumber;
  private string employeetype;

  public void save() {
  new employeerepository().save(this);
  }

  public void calculatetax() {
  new taxcalculator().calculatetax(this);
  }

  public string getemployeeid() {
  return employeeid;
  }

  public void setemployeeid(string employeeid) {
  this.employeeid = employeeid;
  }

  public string getemployeename() {
  return employeename;
  }

  public void setemployeename(string employeename) {
  this.employeename = employeename;
  }

  public string getemployeeaddress() {
  return employeeaddress;
  }

  public void setemployeeaddress(string employeeaddress) {
  this.employeeaddress = employeeaddress;
  }

  public string getcontactnumber() {
  return contactnumber;
  }

  public void setcontactnumber(string contactnumber) {
  this.contactnumber = contactnumber;
  }

  public string getemployeetype() {
  return employeetype;
  }

  public void setemployeetype(string employeetype) {
  this.employeetype = employeetype;
  }

}
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此外，employeerepository 类中发生更改的原因只有一个

变更原因：数据库变更

import java.sql.connection;
import java.sql.drivermanager;
import java.sql.statement;

public class employeerepository {

public void save(employee employee) {
     string insert = myutil.serializeintostring(employee);
    connection connection = null;
    statement statement = null;
    try {
        class.forname("com.mysql.jdbc.driver");
        connection = drivermanager.getconnection("jdbc://mysql://localhost:8080/mydb", "root", "password");
        statement = connection.createstatement();
        statement.execute("insert into employee values (" + insert + ")");

    } catch (exception e) {
        e.printstacktrace();
    }

}

}
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最后，taxcalculator 类中发生变化的原因只有一个

变更原因：税金计算方式变更

public class TaxCalculator {

public void calculateTax(Employee employee) {
    if (employee.getEmployeeType().equals("fulltime")) {
        // tax calculation for full time employee
    } else if (employee.getEmployeeType().equals("contract")) {
        // tax calculation for contract type employee
    }
}

}
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注意：所有 3 个类现在都遵循单一职责原则，因此遵循这两个定义

创建类或任何软件组件时请记住：以高内聚和松散耦合为目标

每个软件组件应该只有一个和一个职责和每个软件组件都应该有且只有一个更改的理由

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