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I'd like to re-implement a method of a Java class. For example, for "hi".length() to return 4. (How) Can I do that?
I know using SomeClass.metaClass I can get a reference to an existing method and define new (or overriding) method, but I can't seem to be able to do that for existing Java methods.
811
According to java, you are only not allowed to change the string object, but you can still modify that object. There are several ways by which you can create a string object and hence declare a string. But for now, we take the simplest way to declare the string, which is as follows; String S= “Hello”;.
You need to copy the string into another, not read-only memory buffer and modify it there. Use strncpy() for copying the string, strlen() for detecting string length, malloc() and free() for dynamically allocating a buffer for the new string. Show activity on this post. The malloc needs 1 more byte.
String are immutable in Java. You can't change them. You need to create a new string with the character replaced.
Python strings are "immutable" which means they cannot be changed after they are created (Java strings also use this immutable style). Since strings can't be changed, we construct *new* strings as we go to represent computed values.
Using Groovy, you can replace any method (even those of final classes) with your own implementation. Method replacement in Groovy uses the meta-object protocol, not inheritance.
Here's the example you requested, i.e. how to make String.length() always return 4
// Redefine the method
String.metaClass.invokeMethod = { name, args ->
def metaMethod = delegate.metaClass.getMetaMethod(name, args)
def result = metaMethod.invoke(delegate, args)
name == 'length' ? 4 : result
}
// Test it
assert "i_do_not_have_4_chars".length() == 4
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