里氏替换原则

定义:子类对象能够替换程序中父类对象出现的任何地方，并且*保证原来程序的逻辑行为不变及正确性不被破坏*。

public class Transporter {private HttpClient httpClient;public Transporter(HttpClient httpClient) {this.httpClient = httpClient;}public Response sendRequest(Request request) {// ...use httpClient to send request}
}public class SecurityTransporter extends Transporter {private String appId;private String appToken;public SecurityTransporter(HttpClient httpClient, String appId, String appToken) {super(httpClient);this.appId = appId;this.appToken = appToken;}@Overridepublic Response sendRequest(Request request) {if (StringUtils.isNotBlank(appId) && StringUtils.isNotBlank(appToken)) {request.addPayload("app-id", appId);request.addPayload("app-token", appToken);}return super.sendRequest(request);}
}public class Demo {    public void demoFunction(Transporter transporter) {    Reuqest request = new Request();//...省略设置request中数据值的代码...Response response = transporter.sendRequest(request);//...省略其他逻辑...}
}// 里式替换原则
Demo demo = new Demo();
demo.demofunction(new SecurityTransporter(/*省略参数*/););

与多态的区别，多态可以改变父类的正确性例如

// 改造前：
public class SecurityTransporter extends Transporter {//...省略其他代码..@Overridepublic Response sendRequest(Request request) {if (StringUtils.isNotBlank(appId) && StringUtils.isNotBlank(appToken)) {request.addPayload("app-id", appId);request.addPayload("app-token", appToken);}return super.sendRequest(request);}
}// 改造后：
public class SecurityTransporter extends Transporter {//...省略其他代码..@Overridepublic Response sendRequest(Request request) {if (StringUtils.isBlank(appId) || StringUtils.isBlank(appToken)) {throw new NoAuthorizationRuntimeException(...);}request.addPayload("app-id", appId);request.addPayload("app-token", appToken);return super.sendRequest(request);}
}

说明:改造后的代码改变了源代码的正确性，使结果出现了多种可能