INVOKEINTERFACE

INVOKEINTERFACE is an instruction in the Java Virtual Machine (JVM) bytecode. It is used to invoke an instance method on an object, where the actual method to be executed is determined at runtime based on the object's runtime type, rather than its compile-time type. This is a key mechanism for achieving polymorphism in Java.

When the JVM encounters an INVOKEINTERFACE instruction, it first looks up the method identified by the instruction's operands on the runtime class of the object. If the method is found in the object's class or any of its superclasses, that specific method is executed. If the method is not found directly, the JVM will search the interfaces implemented by the object's class. This dynamic lookup ensures that the correct method implementation is called, even if the variable holding the object is declared with a more general type.

INVOKEINTERFACE is distinct from other invocation instructions like INVOKEVIRTUAL and INVOKESTATIC. INVOKEVIRTUAL is also used for instance method invocation but is primarily for concrete methods defined in classes, while INVOKEINTERFACE is specifically for methods declared in interfaces. INVOKESTATIC is used for static methods, which are associated with the class itself rather than an instance. The use of INVOKEINTERFACE is fundamental to Java's object-oriented design, allowing for flexible and extensible code.