org.apache.bcel.verifier.structurals

Class OperandStack


public class OperandStack
extends java.lang.Object

This class implements a stack used for symbolic JVM stack simulation. [It's used an an operand stack substitute.] Elements of this stack are org.apache.bcel.generic.Type objects.
Version:
$Id: OperandStack.java,v 1.2 2002/08/02 11:57:51 enver Exp $
Author:
Enver Haase

Constructor Summary

OperandStack(int maxStack)
Creates an empty stack with a maximum of maxStack slots.
OperandStack(int maxStack, ObjectType obj)
Creates an otherwise empty stack with a maximum of maxStack slots and the ObjectType 'obj' at the top.

Method Summary

void
clear()
Clears the stack.
protected Object
clone()
Returns a deep copy of this object; that means, the clone operates on a new stack.
boolean
equals(Object o)
Returns true if and only if this OperandStack equals another, meaning equal lengths and equal objects on the stacks.
OperandStack
getClone()
Returns a (typed!) clone of this.
void
initializeObject(UninitializedObjectType u)
Replaces all occurences of u in this OperandStack instance with an "initialized" ObjectType.
boolean
isEmpty()
Returns true IFF this OperandStack is empty.
int
maxStack()
Returns the number of stack slots this stack can hold.
void
merge(OperandStack s)
Merges another stack state into this instance's stack state.
Type
peek()
Returns the element on top of the stack.
Type
peek(int i)
Returns the element that's i elements below the top element; that means, iff i==0 the top element is returned.
Type
pop()
Returns the element on top of the stack.
Type
pop(int i)
Pops i elements off the stack.
void
push(Type type)
Pushes a Type object onto the stack.
int
slotsUsed()
Returns the number of stack slots used.
String
toString()
Returns a String representation of this OperandStack instance.

Constructor Details

OperandStack

public OperandStack(int maxStack)
Creates an empty stack with a maximum of maxStack slots.

OperandStack

public OperandStack(int maxStack,
                    ObjectType obj)
Creates an otherwise empty stack with a maximum of maxStack slots and the ObjectType 'obj' at the top.

Method Details

clear

public void clear()
Clears the stack.

clone

protected Object clone()
Returns a deep copy of this object; that means, the clone operates on a new stack. However, the Type objects on the stack are shared.

equals

public boolean equals(Object o)
Returns true if and only if this OperandStack equals another, meaning equal lengths and equal objects on the stacks.

getClone

public OperandStack getClone()
Returns a (typed!) clone of this.
See Also:
clone()

initializeObject

public void initializeObject(UninitializedObjectType u)
Replaces all occurences of u in this OperandStack instance with an "initialized" ObjectType.

isEmpty

public boolean isEmpty()
Returns true IFF this OperandStack is empty.

maxStack

public int maxStack()
Returns the number of stack slots this stack can hold.

merge

public void merge(OperandStack s)
Merges another stack state into this instance's stack state. See the Java Virtual Machine Specification, Second Edition, page 146: 4.9.2 for details.

peek

public Type peek()
Returns the element on top of the stack. The element is not popped off the stack!

peek

public Type peek(int i)
Returns the element that's i elements below the top element; that means, iff i==0 the top element is returned. The element is not popped off the stack!

pop

public Type pop()
Returns the element on top of the stack. The element is popped off the stack.

pop

public Type pop(int i)
Pops i elements off the stack. ALWAYS RETURNS "null"!!!

push

public void push(Type type)
Pushes a Type object onto the stack.

slotsUsed

public int slotsUsed()
Returns the number of stack slots used.

toString

public String toString()
Returns a String representation of this OperandStack instance.