java this 代替,有人可以推荐Java 8模式来代替switch语句吗?

- 日理万妓 2022-08-29 14:46 17阅读 0赞

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I have following code:

public class A \{

private String type;

String getType() \{ return type;\}

Now in many code places I have code like this

switch (a.geType()) \{

case "A" : return new Bla();

case "B" : return new Cop();

or somewhere else

switch (a.geType()) \{

case "A" : return new Coda();

case "B" : return new Man();

(Note that I know I should use an Enumeration in production code).

What I want to achive is that when a new type is added to class A the compiler should flag all the switch statements that need to be adjusted?

Is there a java idiomatic way to do this?

解决方案

when a new type is added to class A the compiler should flag all the switch statements that need to be adjusted?

A good approach to this would be replacing switch statements with a more robust implementation of multiple dispatch, such as the Visitor Pattern:

interface VisitorOfA \{

Object visitA(A a);

Object visitB(B b);

class A \{

Object accept(VisitorOfA visitor) \{

return visitor.visitA(this);

class B extends A \{

Object accept(VisitorOfA visitor) \{

return visitor.visitB(this);

With this infrastructure in place, you can remove your switch statements, replacing them with implementations of the visitor:

Object res = a.accept(new VisitorOfA() \{

public Object visitA(A a) \{ return new Bla(); \}

public Object visitB(B b) \{ return new Cop(); \}

\});

When you add a new subtype to A, say, class C, all you need to do is adding a new method to VisitorOfA:

Object visitC(C c);

Now the compiler will spot all places where this new method has not been implemented, helping you avoid problems at runtime.

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java this 代替,有人可以推荐Java 8模式来代替switch语句吗?

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