Class OperandStack

java.lang.Object
org.apache.bcel.verifier.structurals.OperandStack
All Implemented Interfaces:
Cloneable
public class OperandStack extends Object implements 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

    Modifier and Type
    Method
    Description
    void
    clear()
    Clears the stack.
    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()
    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.
    String
    toString()
    Returns a String representation of this OperandStack instance.

    Methods inherited from class Object

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

  • Constructor Details

    • 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 Details

    • clear

      public void clear()
      Clears the stack.

    • clone

      public 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 Object

    • 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.
      Overrides:
      equals in class Object

    • getClone

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

    • hashCode

      public int hashCode()
      Gets the hash code.
      Overrides:
      hashCode in class 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:

    • toString

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