instanceof

instanceof
indexbyte1
indexbyte2

Determine if object is of given type

Forms
instanceof = 193 (0xc1)

Stack
..., objectref ..., result

Description
The objectref, which must be of type reference, is popped from the operand stack. The unsigned indexbyte1 and indexbyte2 are used to construct an index into the constant pool of the current class (§3.6), where the value of the index is (indexbyte1 << 8) | indexbyte2. The item at that index in the constant pool must be a CONSTANT_Class (§4.4.1), a symbolic reference to a class, array, or interface. The symbolic reference is resolved (§5.1).

If objectref is not null and is an instance of the resolved class, array, or interface, the instanceof instruction pushes an int result of 1 as an int on the operand stack. Otherwise, it pushes an int result of 0.

The following rules are used to determine whether an objectref that is not null is an instance of the resolved type: If S is the class of the object referred to by objectref and T is the resolved class, array, or interface type, instanceof determines whether objectref is an instance of T as follows:

• If S is an ordinary (non-array) class, then:
  • If T is a class type, then S must be the same class (§2.8.1) as T or a subclass of T.
  • If T is an interface type, then S must implement (§2.13) interface T.
• If S is a class representing the array type SC[], that is, an array of components of type SC, then:
  • If T is a class type, then T must be Object (§2.4.6).
  • If T is an array type TC[], that is, an array of components of type TC, then one of the following must be true:
    • TC and SC are the same primitive type (§2.4.1).
    • TC and SC are reference types (§2.4.5), and type SC can be cast to TC by these runtime rules.

Linking Exceptions
During resolution of the CONSTANT_Class constant pool item, any of the exceptions documented in §5.1 can be thrown.

Notes
The instanceof instruction is fundamentally very similar to the checkcast instruction. It differs in its treatment of null, its behavior when its test fails (checkcast throws an exception, instanceof pushes a result code), and its effect on the operand stack.

Determine if object is of given type

Forms
instanceof = 193 (0xc1)

Stack
..., objectref ..., result

Description
The objectref, which must be of type reference, is popped from the operand stack. The unsigned indexbyte1 and indexbyte2 are used to construct an index into the constant pool of the current class (§3.6), where the value of the index is (indexbyte1 << 8) | indexbyte2. The item at that index in the constant pool must be a CONSTANT_Class (§4.4.1), a symbolic reference to a class, array, or interface. The symbolic reference is resolved (§5.1).

If objectref is not null and is an instance of the resolved class, array, or interface, the instanceof instruction pushes an int result of 1 as an int on the operand stack. Otherwise, it pushes an int result of 0.

The following rules are used to determine whether an objectref that is not null is an instance of the resolved type: If S is the class of the object referred to by objectref and T is the resolved class, array, or interface type, instanceof determines whether objectref is an instance of T as follows: