[groovy] mop meta object protocol and meta programming (Introduction to groovyobject interface | introduction to metaclass | implementation of class methods using groovyobject invokemethod)

One 、GroovyObject Interface profile

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In class , If you don't realize a Method perhaps Member attribute , You can use Metaprogramming Replace in class Method or property ;

When compiling bytecode files , Every Groovy Classes will be compiled into GroovyObject Interface object ;

/** *  be-all  Groovy  Classes must implement interfaces  * <p> *  stay Java Used in the world Groovy Objects are especially convenient . */public interface GroovyObject { 
        /** * Invokes the given method. * * @param name  Method name to execute  * @param args  Method call method parameters  * @return  The return method executes the return value  */    @Internal //  Marked as internal just for backward compatibility , e.g. AbstractCallSite.createGroovyObjectGetPropertySite  Will check the  `isMarkedInternal`    default Object invokeMethod(String name, Object args) { 
            return getMetaClass().invokeMethod(this, name, args);    }    /** *  Retrieve attribute values . * * @param propertyName  The attribute name  * @return  Return the found attribute value  */    @Internal //  Marked as internal just for backward compatibility , e.g. AbstractCallSite.createGroovyObjectGetPropertySite will check `isMarkedInternal`    default Object getProperty(String propertyName) { 
            return getMetaClass().getProperty(this, propertyName);    }    /** *  Set the given property to the new value . * * @param propertyName  Set the property name of  * @param newValue  new property  */    @Internal //  Marked as internal just for backward compatibility , e.g. AbstractCallSite.createGroovyObjectGetPropertySite will check `isMarkedInternal`    default void setProperty(String propertyName, Object newValue) { 
            getMetaClass().setProperty(this, propertyName, newValue);    }    /** *  Returns the metaclass of a given class . * * @return  Metaclass of this instance  */    MetaClass getMetaClass();    /** *  It is allowed to replace metaclasses with derived implementations . * * @param metaClass  New metaclass  */    void setMetaClass(MetaClass metaClass);}

Two 、MetaClass brief introduction

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MetaClass Metaclasses can be used to implement Metaprogramming Of Methods to inject , Method intercept , Synthetic delegation Wait for the operation ;

/** * Groovy The metaclass in defines any given Groovy or Java Class . *  Metaclass interface defines two parts . *  client  API, It's through ExtendeMetaObjectProtocol Interface  *  and Groovy The contract of the runtime system defines . * *  Usually , The compiler and Groovy The runtime engine interacts with methods on this class , *  The metaclass client and MetaObjectProtocol Interface defined method interaction  * * @see MetaClassImpl * @see groovy.lang.MetaObjectProtocol */public interface MetaClass extends MetaObjectProtocol { 
    }

3、 ... and 、 Use GroovyObject#invokeMethod Execute class methods

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Define a class , Define in it hello Method , You can call the method directly , It can also be done through GroovyObject#invokeMethod Execute the method ;

Code example :

class Student { 
        def name;    def hello() { 
            println "Hello ${name}"    }}def student = new Student(name: "Tom")//  Call directly  hello  Method student.hello()//  adopt  GroovyObject#invokeMethod  call  hello  Method //  The second parameter is the function parameter  ,  If  void  Then in  nullstudent.invokeMethod("hello", null)

Execution results :

Hello TomHello Tom