checkcast

• 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.

Runtime Exception
Otherwise, if objectref cannot be cast to the resolved class, array, or interface type, the checkcast instruction throws a ClassCast-Exception.

Notes
The checkcast instruction is very similar to the instanceof 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.

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Java Virtual Machine Specification (HTML generated by dkramer on February 25, 1997)
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