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Method invocation proceeds with the following steps, in order:
If the underlying method is static, then the specified object argument is ignored. It may be null.
Otherwise, the method is an instance method. If the specified object argument is null, the invocation throws a NullPointerException. Otherwise, if the specified object argument is not an instance of the class or interface declaring the underlying method, the invocation throws an IllegalArgumentException.
If this Method object enforces Java language access control and the underlying method is inaccessible, the invocation throws an IllegalAccessException.
If the number of actual parameters supplied via args is different from the number of formal parameters required by the underlying method, the invocation throws an IllegalArgumentException.
For each actual parameter in the supplied args array:
If the corresponding formal parameter has a primitive type, an unwrapping conversion is attempted to convert the object value to a value of a primitive type. If this attempt fails, the invocation throws an IllegalArgumentException.
If, after possible unwrapping, the parameter value cannot be converted to the corresponding formal parameter type by an identity or widening conversion, the invocation throws an IllegalArgumentException.
If the underlying method is an instance method, it is invoked using dynamic method lookup as documented in The Java Language Specification, section 15.11.4.4; in particular, overriding based on the runtime type of the target object will occur.
If the underlying method is static, it is invoked as exactly the method on the declaring class.
Control transfers to the underlying method. If the method completes abruptly by throwing an exception, the exception is placed in an InvocationTargetException and thrown in turn to the caller of invoke.
If the method completes normally, the value it returns is returned to the caller of invoke; if the value has a primitive type, it is first appropriately wrapped in an object. If the underlying method return type is void, the invocation returns null.