org.apache.bcel.verifier.structurals

Class OperandStack

public class OperandStack extends 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 386056 2006-03-15 11:31:56Z tcurdt $

Author: Enver Haase

Field Summary
int	maxStack The maximum number of stack slots this OperandStack instance may hold.
ArrayList	stack We hold the stack information here.

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!)
int	hashCode()
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	size() Returns the size of this OperandStack; that means, how many Type objects there are.
int	slotsUsed() Returns the number of stack slots used.
String	toString() Returns a String representation of this OperandStack instance.

Field Detail

maxStack

private int maxStack

The maximum number of stack slots this OperandStack instance may hold.

stack

private ArrayList stack

We hold the stack information here.

Constructor Detail

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 Detail

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.

hashCode

public int hashCode()

Returns: a hash code value for the object.

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.

size

public int size()

Returns the size of this OperandStack; that means, how many Type objects there are.

slotsUsed

public int slotsUsed()

Returns the number of stack slots used.

toString

public String toString()

Returns a String representation of this OperandStack instance.