Package org.apache.bcel.verifier.structurals

Class OperandStack

  • All Implemented Interfaces:
    java.lang.Cloneable
    public class OperandStack
extends java.lang.Object
implements java.lang.Cloneable
    This class implements a stack used for symbolic JVM stack simulation. [It's used as an operand stack substitute.] Elements of this stack are Type objects.

    • Constructor Summary

      Constructors 
      Constructor Description
      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

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void clear()
      Clears the stack.
      java.lang.Object clone()
      Returns a deep copy of this object; that means, the clone operates on a new stack.
      boolean equals​(java.lang.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.
      int hashCode()
      Gets the hash code.
      void initializeObject​(UninitializedObjectType u)
      Replaces all occurrences 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 depth)
      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 count)
      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.
      java.lang.String toString()
      Returns a String representation of this OperandStack instance.

      • Methods inherited from class java.lang.Object

        finalize, getClass, notify, notifyAll, wait, wait, wait

    • Constructor Detail

      • OperandStack

        public OperandStack​(int maxStack)
        Creates an empty stack with a maximum of maxStack slots.
        Parameters:
        maxStack - The maximum stack size.

      • 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.
        Parameters:
        maxStack - The maximum stack size.
        obj - The object type to place at the top.

    • Method Detail

      • clear

        public void clear()
        Clears the stack.

      • clone

        public java.lang.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.
        Overrides:
        clone in class java.lang.Object

      • equals

        public boolean equals​(java.lang.Object o)
        Returns true if and only if this OperandStack equals another, meaning equal lengths and equal objects on the stacks.
        Overrides:
        equals in class java.lang.Object

      • getClone

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

      • hashCode

        public int hashCode()
        Gets the hash code.
        Overrides:
        hashCode in class java.lang.Object
        Returns:
        A hash code value for the object.

      • initializeObject

        public void initializeObject​(UninitializedObjectType u)
        Replaces all occurrences of u in this OperandStack instance with an "initialized" ObjectType.
        Parameters:
        u - The uninitialized object type.

      • isEmpty

        public boolean isEmpty()
        Returns true IFF this OperandStack is empty.
        Returns:
        true if empty, false otherwise.

      • maxStack

        public int maxStack()
        Returns the number of stack slots this stack can hold.
        Returns:
        The maximum stack size.

      • 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.
        Parameters:
        s - The stack to merge.

      • peek

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

      • peek

        public Type peek​(int depth)
        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!
        Parameters:
        depth - The depth.
        Returns:
        The element at the specified depth.

      • pop

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

      • pop

        public Type pop​(int count)
        Pops i elements off the stack. Always returns null.
        Parameters:
        count - The number of elements to pop.
        Returns:
        Always returns null.

      • push

        public void push​(Type type)
        Pushes a Type object onto the stack.
        Parameters:
        type - The type to push.

      • size

        public int size()
        Returns the size of this OperandStack; that means, how many Type objects there are.
        Returns:
        The stack size.

      • slotsUsed

        public int slotsUsed()
        Returns the number of stack slots used.
        Returns:
        The number of slots used.
        See Also:
        maxStack()

      • toString

        public java.lang.String toString()
        Returns a String representation of this OperandStack instance.
        Overrides:
        toString in class java.lang.Object
        Returns:
        string representation.