javassist.bytecode.analysis
Class Type

java.lang.Object
  extended by javassist.bytecode.analysis.Type
Direct Known Subclasses:
MultiArrayType, MultiType

public class Type
extends java.lang.Object

Represents a JVM type in data-flow analysis. This abstraction is necessary since a JVM type not only includes all normal Java types, but also a few special types that are used by the JVM internally. See the static field types on this class for more info on these special types. All primitive and special types reuse the same instance, so identity comparison can be used when examining them. Normal java types must use equals(Object) to compare type instances. In most cases, applications which consume this API, only need to call getCtClass() to obtain the needed type information.

Author:
Jason T. Greene

Field Summary
static Type BOGUS
          Represents a non-accessible value.
static Type BOOLEAN
          Represents the boolean primitive type
static Type BYTE
          Represents the byte primitive type
static Type CHAR
          Represents the char primitive type
static Type CLONEABLE
          Represents the java.lang.Coneable reference type
static Type DOUBLE
          Represents the double primitive type
static Type FLOAT
          Represents the float primitive type
static Type INTEGER
          Represents the integer primitive type
static Type LONG
          Represents the long primitive type
static Type OBJECT
          Represents the java.lang.Object reference type
static Type RETURN_ADDRESS
          Represents an internal JVM return address, which is used by the RET instruction to return to a JSR that invoked the subroutine.
static Type SERIALIZABLE
          Represents the java.io.Serializable reference type
static Type SHORT
          Represents the short primitive type
static Type THROWABLE
          Represents the java.lang.Throwable reference type
static Type TOP
          A placeholder used by the analyzer for the second word position of a double-word type
static Type UNINIT
          Represents an unknown, or null type.
static Type VOID
          Represents the void primitive type
 
Method Summary
 boolean equals(java.lang.Object o)
           
static Type get(CtClass clazz)
          Obtain the Type for a given class.
 Type getComponent()
          Returns the array component if this type is an array.
 CtClass getCtClass()
          Returns the class this type represents.
 int getDimensions()
          Returns the number of dimensions of this array.
 int getSize()
          Gets the word size of this type.
 boolean isArray()
          Returns whether or not this type is an array.
 boolean isAssignableFrom(Type type)
          Determines whether this type is assignable, to the passed type.
 boolean isReference()
          Returns whether or not this type is a normal java reference, i.e.
 boolean isSpecial()
          Returns whether or not the type is special.
 Type merge(Type type)
          Finds the common base type, or interface which both this and the specified type can be assigned.
 java.lang.String toString()
           
 
Methods inherited from class java.lang.Object
clone, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
 

Field Detail

DOUBLE

public static final Type DOUBLE
Represents the double primitive type


BOOLEAN

public static final Type BOOLEAN
Represents the boolean primitive type


LONG

public static final Type LONG
Represents the long primitive type


CHAR

public static final Type CHAR
Represents the char primitive type


BYTE

public static final Type BYTE
Represents the byte primitive type


SHORT

public static final Type SHORT
Represents the short primitive type


INTEGER

public static final Type INTEGER
Represents the integer primitive type


FLOAT

public static final Type FLOAT
Represents the float primitive type


VOID

public static final Type VOID
Represents the void primitive type


UNINIT

public static final Type UNINIT
Represents an unknown, or null type. This occurs when aconst_null is used. It is important not to treat this type as java.lang.Object, since a null can be assigned to any reference type. The analyzer will replace these with an actual known type if it can be determined by a merged path with known type information. If this type is encountered on a frame then it is guaranteed to be null, and the type information is simply not available. Any attempts to infer the type, without further information from the compiler would be a guess.


RETURN_ADDRESS

public static final Type RETURN_ADDRESS
Represents an internal JVM return address, which is used by the RET instruction to return to a JSR that invoked the subroutine.


TOP

public static final Type TOP
A placeholder used by the analyzer for the second word position of a double-word type


BOGUS

public static final Type BOGUS
Represents a non-accessible value. Code cannot access the value this type represents. It occurs when bytecode reuses a local variable table position with non-mergable types. An example would be compiled code which uses the same position for a primitive type in one branch, and a reference type in another branch.


OBJECT

public static final Type OBJECT
Represents the java.lang.Object reference type


SERIALIZABLE

public static final Type SERIALIZABLE
Represents the java.io.Serializable reference type


CLONEABLE

public static final Type CLONEABLE
Represents the java.lang.Coneable reference type


THROWABLE

public static final Type THROWABLE
Represents the java.lang.Throwable reference type

Method Detail

get

public static Type get(CtClass clazz)
Obtain the Type for a given class. If the class is a primitive, the the unique type instance for the primitive will be returned. Otherwise a new Type instance representing the class is returned.

Parameters:
clazz - The java class
Returns:
a type instance for this class

getSize

public int getSize()
Gets the word size of this type. Double-word types, such as long and double will occupy two positions on the local variable table or stack.

Returns:
the number of words needed to hold this type

getCtClass

public CtClass getCtClass()
Returns the class this type represents. If the type is special, null will be returned.

Returns:
the class for this type, or null if special

isReference

public boolean isReference()
Returns whether or not this type is a normal java reference, i.e. it is or extends java.lang.Object.

Returns:
true if a java reference, false if a primitive or special

isSpecial

public boolean isSpecial()
Returns whether or not the type is special. A special type is one that is either used for internal tracking, or is only used internally by the JVM.

Returns:
true if special, false if not

isArray

public boolean isArray()
Returns whether or not this type is an array.

Returns:
true if an array, false if not

getDimensions

public int getDimensions()
Returns the number of dimensions of this array. If the type is not an array zero is returned.

Returns:
zero if not an array, otherwise the number of array dimensions.

getComponent

public Type getComponent()
Returns the array component if this type is an array. If the type is not an array null is returned.

Returns:
the array component if an array, otherwise null

isAssignableFrom

public boolean isAssignableFrom(Type type)
Determines whether this type is assignable, to the passed type. A type is assignable to another if it is either the same type, or a sub-type.

Parameters:
type - the type to test assignability to
Returns:
true if this is assignable to type, otherwise false

merge

public Type merge(Type type)
Finds the common base type, or interface which both this and the specified type can be assigned. If there is more than one possible answer, then a MultiType, or a MultiArrayType is returned. Multi-types have special rules, and successive merges and assignment tests on them will alter their internal state, as well as other multi-types they have been merged with. This method is used by the data-flow analyzer to merge the type state from multiple branches.

Parameters:
type - the type to merge with
Returns:
the merged type

equals

public boolean equals(java.lang.Object o)
Overrides:
equals in class java.lang.Object

toString

public java.lang.String toString()
Overrides:
toString in class java.lang.Object


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