before refactor:
public interface Service {
public void hello(Person p);
}
public class BlackPersonServiceImpl implements Service {
#Override
public void hello(Person p) {
//...
}
}
public class WhitePersonServiceImpl implements Service {
#Override
public void hello(Person p) {
//...
}
}
public class BeforeRefactor {
public static void main(String[] args) {
String str = args[0];
Person p = JSON.parseObject(str, Person.class);
Service service = getServiceFromSpringContainer();
service.hello(p);
}
private static Service getServiceFromSpringContainer() {
//...
return null;
}
}
after refactor:
public interface Service {
public void hello(String str);
}
public class WhitePersonServiceImpl implements Service {
#Override
public void hello(String str) {
Person person = JSON.parseObject(str, Person.class);
//do something to person...
//...
}
}
public class AfterRefactor {
public static void main(String[] args) {
String str = args[0];
Service service = getServiceFromSpringContainer();
service.hello(str);
}
private static Service getServiceFromSpringContainer() {
//...
return null;
}
}
That's what I want(I think "pull down" is not the "right" word to describe it...).
I tried "introduce parameter object" in eclipse, and it does not work.
There are many implementations of "Service". I dont want to change them one by one.
Is there a good way to solve this problem?
Thanks!
You can do it somewhat for a single class and a single method (although it's akward and a succession of small refactoring steps), but not across several types at the same time.
Related
I like to have a Drive class where all files and folders for a project are managed.
My first attempt was pretty easy like a lot of functions (most of them with arguments).
Now I try to make it more fancy because it became more and more annoying to have a lot of functions, in which the desired one can be found. To not have an XY-problem here, I start with my dream.
I like to construct the Drive class in a way, so that it is super easy to find a certain file or folder.
If you look in the main function, I can find every needed file by writing a point and look which subclasses/methods are proposed to continue, till I find it and add .str to it. At every point, only the subclasses/methods will be proposed which makes sense at this point.
It almost works! It is more complicated to write and maintain as the first approach, but If I use it very often, it could be worth it.
I can:
go into subfolders
go into subfolders with name inside the argument
But there is an error if I define a fixed-name-subfolder of a fluid-name-folder like in the code below.
Now my questions:
how can I change the code so the main Function doesn't show this error?
would you recommend a completely different approach to the "make it easy to find strings inside a huge list of strings via making collections inside collections... of strings"-problem?
package utilities;
public class Drive_draft {
private static final String fs = System.getProperty("file.separator");
public static final String str = System.getProperty("user.home").concat(fs);
public static class IeCreation {
public static final String str = Drive_draft.str.concat(".meetings").concat(fs);
public static class Abstract {
public static final String str = IeCreation.str.concat("Abstracts").concat(fs);
}
public static class Meeting {
public static final String str = IeCreation.str.concat("Ueberordnungen").concat(fs);
}
}
public static class MetsSIPs {
public static final String str = Drive_draft.str.concat("workspace").concat(fs).concat("metsSIPs").concat(fs);
public static class preSIPs {
public static final String str = MetsSIPs.str.concat("preSIPs").concat(fs);
}
public static class RosettaInstance {
private static class MaterialflowId {
public static String str;
private static class ProducerId {
public static String str;
private static class Abstract {
public static String str;
public static class Mets {
public static final String str = Abstract.str.concat("content").concat(fs).concat("ie1.xml");
}
}
private static class Meeting {
public static String str;
}
public static Abstract Abstract (String value) {
Abstract ret = new Abstract();
ProducerId.Abstract.str = str.concat(value).concat(fs);
return ret;
}
public static Meeting Meeting (String value) {
Meeting ret = new Meeting();
ProducerId.Meeting.str = str.concat(value).concat(fs);
return ret;
}
}
public static ProducerId ProducerId (String value) {
ProducerId ret = new ProducerId();
MaterialflowId.ProducerId.str = str.concat(value).concat(fs);
return ret;
}
}
public static MaterialflowId MaterialflowId (String value) {
MaterialflowId ret = new MaterialflowId();
MaterialflowId.str = str.concat(value).concat(fs);
return ret;
}
}
public static class Dev extends RosettaInstance {
public static final String str = MetsSIPs.str.concat("dev").concat(fs);
}
public static class Test extends RosettaInstance {
public static final String str = MetsSIPs.str.concat("test").concat(fs);
}
public static class Prod extends RosettaInstance{
public static final String str = MetsSIPs.str.concat("prod").concat(fs);
}
}
#SuppressWarnings("static-access")
public static void main(String[] args) {
System.out.println(Drive_draft.MetsSIPs.Dev.str);
System.out.println(Drive_draft.MetsSIPs.Dev.MaterialflowId("1").str);
System.out.println(Drive_draft.MetsSIPs.Dev.MaterialflowId("2").str);
System.out.println(Drive_draft.MetsSIPs.Dev.MaterialflowId("1").ProducerId("t").str);
System.out.println(Drive_draft.MetsSIPs.Dev.MaterialflowId("1").ProducerId("t").Abstract("est").str);
System.out.println(Drive_draft.MetsSIPs.Dev.MaterialflowId("1").ProducerId("t").Meeting("oast").str);
System.out.println(Drive_draft.MetsSIPs.Dev.MaterialflowId("1").ProducerId("t").Abstract("est").Mets.str); //Error: Mets cannot be resolved or is not a field
}
}
You can encode your "directory" structure with interfaces, with each interface declaring what the user can do next. Then the implementation can use a StringBuilder to just append the appropriate snippets and keep returning this.
// PathBuilderInterfaces.java
public class PathBuilderInterfaces {
public interface Buildable {
String build();
}
public interface Drive extends Buildable {
IeCreation ieCreation();
MetsSIPs metsSIPs();
}
public interface IeCreation extends Buildable {
String ieCreationAbstract();
String meeting();
}
public interface MetsSIPs extends Buildable {
RosettaInstance dev();
RosettaInstance test();
RosettaInstance prod();
}
public interface RosettaInstance extends Buildable {
MaterialFlowId materialFlowId(String value);
}
public interface MaterialFlowId extends Buildable {
ProducerId producerId(String value);
}
public interface ProducerId extends Buildable {
Abstract producerIdAbstract(String value);
String meeting(String value);
}
public interface Abstract extends Buildable {
String mets();
}
}
// PathBuilder.java
import static com.example.somepackage.PathBuilderInterfaces.*;
public class PathBuilder implements Drive, IeCreation, MetsSIPs, RosettaInstance, MaterialFlowId, ProducerId, Abstract{
private StringBuilder builder = new StringBuilder(str);
private static final String fs = System.getProperty("file.separator");
public static final String str = System.getProperty("user.home").concat(fs);
public static Drive drive() {
return new PathBuilder();
}
#Override
public String build() {
return builder.toString();
}
#Override
public IeCreation ieCreation() {
builder.append(".meetings").append(fs);
return this;
}
#Override
public MetsSIPs metsSIPs() {
builder.append("workspace").append(fs).append("metsSIPs").append(fs);
return this;
}
#Override
public RosettaInstance dev() {
builder.append("dev").append(fs);
return this;
}
#Override
public RosettaInstance test() {
builder.append("test").append(fs);
return this;
}
#Override
public RosettaInstance prod() {
builder.append("prod").append(fs);
return this;
}
#Override
public MaterialFlowId materialFlowId(String value) {
builder.append(value).append(fs);
return this;
}
#Override
public ProducerId producerId(String value) {
builder.append(value).append(fs);
return this;
}
#Override
public Abstract producerIdAbstract(String value) {
builder.append(value).append(fs);
return this;
}
#Override
public String meeting(String value) {
builder.append(value).append(fs);
return build();
}
#Override
public String mets() {
builder.append("content").append(fs).append("ie1.xml");
return build();
}
#Override
public String ieCreationAbstract() {
builder.append("Abstracts").append(fs);
return build();
}
#Override
public String meeting() {
builder.append("Ueberordnungen").append(fs);
return build();
}
}
Usage:
// in a main method somewhere
System.out.println(
PathBuilder.drive()
.metsSIPs()
.dev()
.materialFlowId("1")
.producerId("t")
.producerIdAbstract("est")
.mets());
I'm trying to get rid of big switch statement from my code and I thought that Strategy pattern based on my existing enum would be nice. The concept is like:
public class MyStrategy {
public MyStrategy() {
Option.Option1.setMethodToExecute(this::action1);
Option.Option2.setMethodToExecute(this::action2);
}
public void executeChoosenMethod(int i) {
Option.values()[i].execute();
// instead of
// switch(convertItoOption()) {
// case Option1:...
// case Option2:...
// }
}
private void action1() {
System.out.println("action1");
}
private void action2() {
System.out.println("action2");
}
private enum Option {
Option1, Option2;
private InvokeAction methodToExecute;
public void setMethodToExecute(InvokeAction methodToExecute) {
this.methodToExecute = methodToExecute;
}
public void execute() {
methodToExecute.execute();
}
}
#FunctionalInterface
private interface InvokeAction {
void execute();
}
}
so I can use it like:
public class StrategyTest {
public static void main(String[] args) {
MyStrategy strategy = new MyStrategy();
//user choose 0 or 1
strategy.executeChoosenMethod(0);
strategy.executeChoosenMethod(1);
}
}
but I don't like this part with Option.Option1.setMethodToExecute(this::action1); since my enum has more and more options and I would like to have all of this inside enum. What would be perfect is something like this:
public class MyStrategy {
public void executeChoosenMethod(int i) {
Option.values()[i].execute();
}
private void action1() {
System.out.println("action1");
}
private void action2() {
System.out.println("action2");
}
private enum Option {
Option1(MyStrategy.this::action1),
Option2(MyStrategy.this::action2);
private InvokeAction methodToExecute;
private Option(InvokeAction method) {
methodToExecute = method;
}
public void execute() {
methodToExecute.execute();
}
}
#FunctionalInterface
private interface InvokeAction {
void execute();
}
}
but this is impossible since enum is static and I don't have access to enclosing instance by MyStrategy.this. I need enum, because I have set of options and it is convenient to use methods like values() or valueOf(), but what I would like to have is single line invoke instead of growing switch.
Do you have any ideas how to achieve sometghing like this or is there any workaround to make this enum constructor call possible Option1(MyStrategy.this::action1) ?
With enums you could implement it like this:
public class MyStrategy {
public void executeChoosenMethod(int i) {
Option.values()[i].execute(this);
}
private void action1() {
System.out.println("action1");
}
private void action2() {
System.out.println("action2");
}
private enum Option {
Option1(MyStrategy::action1),
Option2(MyStrategy::action2);
private InvokeAction methodToExecute;
private Option(InvokeAction method) {
methodToExecute = method;
}
public void execute(MyStrategy s) {
methodToExecute.execute(s);
}
}
#FunctionalInterface
private interface InvokeAction {
void execute(MyStrategy s);
}
}
This uses the fact the with lambdas you can make method references to arbitrary instance methods and call them on a specific instance by passing in the instance as first parameter.
you're right. This isn't possible with enum. But why not just use a good old class:
public class MyStrategy {
public MyStrategy() {
buildUp();
}
public void executeChoosenMethod(int i) {
actions.get(i).execute();
}
private void action1() {
System.out.println("action1");
}
private void action2() {
System.out.println("action2");
}
private List<InvokeAction> actions = new ArrayList<>();
private void buildUp() {
actions.add(this::action1);
actions.add(this::action2);
}
#FunctionalInterface
private interface InvokeAction {
void execute();
}
}
Consider a method
public void doSomething(String actionID){
switch (actionID){
case "dance":
System.out.print("I'm dancing");
break;
case "sleep":
System.out.print("I'm sleeping");
break;
default:
System.out.print("I've no idea what I'm doing");
}
The implementation of the method depends on the value of the parameter. Is there a more elegant way to do this, or a different design pattern to replicate the behaviour?
If the caller decides what logic is executed by passing different strings, then why not just have them call different methods:
public void doSomething(String actionID) {...}
...
doSomething("dance");
doSomething("sleep");
VS.:
public void dance() {...}
public void sleep() {...}
...
dance();
sleep();
It seems like you're unnecessarily funnelling all the calls into doSomething
But the strings might not always be literals. What if you're taking them from the console?
You could provide static mappings from the strings to the corresponding functions:
class MyClass {
private static final Map<String, Consumer<MyClass>> map = new HashMap<>();
static {
map.put("sleep", MyClass::sleep);
map.put("dance", MyClass::dance);
}
public void doSomething(String actionID) {
map.getOrDefault(actionID, MyClass::doNothing).accept(this);
}
public void dance() {
System.out.print("I'm dancing");
}
public void sleep() {
System.out.print("I'm sleeping");
}
private void doNothing() {
System.out.println("I've no idea what I'm doing");
}
}
This makes scenarios where you have a lot of switch cases a lot cleaner.
Introduce an interface, e.g.
public interface HumanState {
public void tellMeWhatYouAreDoing();
}
encapsulate the logic in different implementations
public class DancingState implements HumanState {
#Override
public void tellMeWhatYouAreDoing() {
System.out.println("I'm dancing");
}
}
public class SleepingState implements HumanState {
#Override
public void tellMeWhatYouAreDoing() {
System.out.println("I'm sleeping");
}
}
public class UnknownState implements HumanState {
#Override
public void tellMeWhatYouAreDoing() {
System.out.println("I've no idea what I'm doing");
}
}
and use a map. E.g.
public class HumanStateExample {
public static void main(String[] args) {
HumanStateExample humanStateExample = new HumanStateExample();
humanStateExample.doSomething("dance");
humanStateExample.doSomething("sleep");
humanStateExample.doSomething("unknown");
}
private final HashMap<String, HumanState> humanStateMap;
public HumanStateExample(){
humanStateMap = new HashMap<String, HumanState>();
humanStateMap.put("dance", new DancingState());
humanStateMap.put("sleep", new SleepingState());
}
public void doSomething(String action) {
HumanState humanState = humanStateMap.get(action);
if(humanState == null){
humanState = new UnknownState();
}
humanState.tellMeWhatYouAreDoing();
}
}
I'm not sure how the pattern is called, but it is very useful if you need to delegate the method call based on more than one parameter:
Create a lot of handlers where each one knows when it is responsible for handling a call. Then just loop through them and invoke the first one matching the parameter.
edit: I renamed the class from FancyParameterActionFactory to FancyParameterActionUtility: it is not a factory, the name was misleading
//Your method, but this time with a complex object, not with a simple string.
public void doSomething(FancyParameterObject fpo){
FancyParameterActionUtility.invokeOn(fpo);
}
//The utility which can handle the complex object and decides what to do.
public class FancyParameterActionUtility{
public Interface FPAHandler{
void invoke(FancyParameterObject fpo);
boolean handles(FancyParameterObject fpo);
}
//Omitted: Different implementations of FPAHandler
public static List<FPAHandler> handlers = new LinkedList<>();
static{
handlers.add(new DanceHandler());
handlers.add(new SleepHandler());
//Omitted: Different implementations of FPAHandler
}
public static void invokeOn(FancyParameterObject fpo){
for(FPAHandler handler:handlers){
if (handler.handles(fpo)){
handler.invoke(fpo);
return;
}
}
//Default-Behavior
}
}
Here is a simple implementation of the command pattern based your sample problem. I define a general AbstractCommand abstract class which contains two methods. The first method, createCommand(), instantiates a command class based on an input string name. This is how you can delegate your string input to create the right type of command. The second method is doAction(), and this is left undefined, to be implemented later on by specific concrete command classes.
public abstract class AbstractCommand {
public static AbstractCommand createCommand(String name) {
try {
String clsName = name + "Command";
Class<?> cls = Class.forName(clsName);
AbstractCommand command = (AbstractCommand) cls.newInstance();
return command;
}
catch (Exception e) {
System.out.println("Something went wrong.");
}
}
public abstract void doAction();
}
public class DanceCommand extends AbstractCommand {
public void doAction() {
System.out.println("I'm dancing");
}
}
public class TestCommandPattern {
public void doSomething(String actionID) {
AbstractCommand cmd = AbstractCommand.createCommand(actionID);
cmd.doAction();
}
public static void main(String[] args) {
TestCommandPattern test = new TestCommandPattern();
test.doSomething("Dance"); // should print "I'm dancing"
}
}
Now that this framework has been setup, you could easily add other commands for the various types of actions in your original problem. For example, you could create a SleepCommand class which would output I'm sleeping, or do whatever action you wish.
Hi ive been reading on some similar topics here but none of them answer my question. Some say you cant even do this which is not a good thing since I cant finnish my course in that case.
Heres som simple code. Think of each block as a separate class.
public interface Interface {
void printMessage(String meddelande);
}
public class Model implements Interface {
String message = "hej!";
public static void main(String[] args) {
Model model1 = new Model();
View view1 = new View();
model1.printMessage(model1.message); //Ska jag anropa funktionen såhär ens?
}
public void printMessage(String str) {
}
}
public class View implements Interface {
printMessage(String str) {
}
}
So, how is it now possible to tel the view to print this string from the model class without the classes knowing about each other? Its not allowed to send a reference of the model-objekt to the view-object. ; (
Define an Interface:
public interface MyInterface {
void printMessage(String str);
}
Define a class that can trigger the notification:
public class ClassNotifier {
MyInterface mInterface;
public ClassNotifier(MyInterface mInterface) {
this.mInterface = mInterface;
}
public void triggerTheMsg(String msg) {
if (mInterface != null) {
mInterface.printMessage(msg);
}
}
}
Define a class that will be informed:
public class InformedClass implements MyInterface {
public static void main(String[] args) throws Exception {
InformedClass c = new InformedClass();
ClassNotifier cn = new ClassNotifier(c);
}
#Override
public void printMessage(String newMsg) {
System.out.println("A new msg is here: " + newMsg);
}
}
How does it works?:
this is named a callback parttern, the class ClassNotifier has a reference to the interface MyInterface, which is impl. by Informed class to, so every time the ClassNotifier calls the method printMessage, the method printMessage in the class Informed will be triggered too.
I advice you to use dependency injection, for example:
public class Model {
String message = "hej!";
Interface printer;
public void Model(Interface printer) {
printer = printer;
}
public static void main(String[] args) {
Model model1 = new Model(new View());
model1.printMessage(model1.message);
}
public void printMessage(String str) {
printer.printMessage(str);
}
}
This question already has an answer here:
Methods in Enums [duplicate]
(1 answer)
Closed 8 years ago.
Right now, I have an enum for a variety of values, and I was wondering if there is any way I would be able to store a method in an enum. For example:
public enum myEnum{
one("first", callFirstMethod),
two("second", callSecondMethod),
three("last", callThirdMethod);
public String message;
public Method met;
myEnum(String m, Method meth){
message = m;
met = meth;
}
}
public class myMethods{
public void callFirstMethod(){
System.out.println("First!");
}
public void callSecondMethod(){
System.out.println("Second!");
}
public void callThirdMethod(){
System.out.println("Third!");
}
}
Then by using something like:
Method method = myEnum.one.callFirstMethod();
To call the method. Is something like this possible? I've tried playing around/looking around on google, and nothing is really turning up. Thank you for the help!
Use an interface and have the interface instance as the second enum parameter, or give it an abstract method that is implemented in the instance. For instance:
enum MyEnum {
ONE("first", new MyInterface() {
#Override
public void commonMethod() {
System.out.println("First!");
}
}) {
#Override
public void abstractEnumMethod() {
System.out.println("abstract enum meuthod, first!");
}
},
TWO("second", new MyInterface() {
#Override
public void commonMethod() {
System.out.println("Second!");
}
}) {
#Override
public void abstractEnumMethod() {
System.out.println("abstract enum meuthod, second!");
}
},
THREE("last", new MyInterface() {
#Override
public void commonMethod() {
System.out.println("Third!");
}
}) {
#Override
public void abstractEnumMethod() {
System.out.println("abstract enum meuthod, third!");
}
};
private String message;
private MyInterface myType;
private MyEnum(String m, MyInterface myType) {
message = m;
this.myType = myType;
}
public String getMessage() {
return message;
}
public MyInterface getMyType() {
return myType;
}
public void enumMethod() {
System.out.println(message);
}
public abstract void abstractEnumMethod();
}
interface MyInterface {
void commonMethod();
}
The answer all depends on what it's you want to achieve. For example, you could provide a common method within you enum and inspect the instance of the enum calling it...
public class TestEnum {
public static void main(String[] args) {
MyEnum.ONE.doStuff();
MyEnum.TWO.doStuff();
MyEnum.THREE.doStuff();
}
public enum MyEnum {
ONE("first"),
TWO("second"),
THREE("last");
public String message;
MyEnum(String m) {
message = m;
}
public void doStuff() {
System.out.println(name());
if (ONE.equals(this)) {
System.out.println("...Do stuff for one");
} else if (TWO.equals(this)) {
System.out.println("...Do stuff for two");
} else if (THREE.equals(this)) {
System.out.println("...Do stuff for three");
}
}
}
}
Which outputs...
one
...Do stuff for one
two
...Do stuff for two
three
...Do stuff for three