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;
}
}
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
浚心时尚购物商城程序
下载
时尚购物程序v1.01、全立体设计。此系统由3个Flash动画为主线（正式版带原文件），设计更形象，网站更有吸引力。这种设计在网店系统内绝无仅有，使您的网店与众不同。2、内置音乐播放器，简单灵活的操作即可完成设置，前台任意调用。并带详细说明文件，一看就懂。合理使用此功能，可使网站更富渲染力。3、支持多图显示，每件产品最多可以上传9张图片。4、后台功能强大，销售管理，财务管理，在线支付平台管理等功能
/**
* 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;
}
}
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();
}
}
}
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
}
}
}
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
