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The Apache Commons Codec package contains simple encoder and decoders for
various formats such as Base64 and Hexadecimal. In addition to these
widely used encoders and decoders, the codec package also maintains a
collection of phonetic encoding utilities.
/*
* Copyright (c) 2005, Graph Builder
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* * Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
*
* * Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* * Neither the name of Graph Builder nor the names of its contributors may be
* used to endorse or promote products derived from this software without
* specific prior written permission.
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
package com.graphbuilder.math;
import com.graphbuilder.struc.Bag;
/**
The class from which all nodes of an expression tree are descendents. Expressions can be evaluated
using the eval method. Expressions that are or have FuncNodes or VarNodes as descendents must provide
a VarMap or FuncMap respectively. Expressions that consist entirely of OpNodes and ValNodes do not
require a VarMap or FuncMap. For Expressions that support children (OpNodes, FuncNodes), a child can
only be accepted provided it currently has no parent, a cyclic reference is not formed, and it is
non-null.
*/
public abstract class Expression {
protected Expression parent = null;
/**
Returns the result of evaluating the expression tree rooted at this node.
*/
public abstract double eval(VarMap v, FuncMap f);
/**
Returns true if this node is a descendent of the specified node, false otherwise. By this
methods definition, a node is a descendent of itself.
*/
public boolean isDescendent(Expression x) {
Expression y = this;
while (y != null) {
if (y == x)
return true;
y = y.parent;
}
return false;
}
/**
Returns the parent of this node. Returns null if this node is the root node of an expression-tree.
*/
public Expression getParent() {
return parent;
}
/**
Protected method used to verify that the specified expression can be included as a child
expression of this node. An expression cannot be included as a child if it is null, it
currently has a parent, or a cyclic reference would be formed.
@throws IllegalArgumentException If the specified expression is not accepted.
*/
protected void checkBeforeAccept(Expression x) {
if (x == null)
throw new IllegalArgumentException("expression cannot be null");
if (x.parent != null)
throw new IllegalArgumentException("expression must be removed parent");
if (isDescendent(x))
throw new IllegalArgumentException("cyclic reference");
}
/**
Returns an array of exact length of the variable names contained in the expression tree rooted at this node.
*/
public String[] getVariableNames() {
return getTermNames(true);
}
/**
Returns an array of exact length of the function names contained in the expression tree rooted at this node.
*/
public String[] getFunctionNames() {
return getTermNames(false);
}
private String[] getTermNames(boolean varNames) {
Bag b = new Bag();
getTermNames(this, b, varNames);
String[] arr = new String[b.size()];
for (int i = 0; i < arr.length; i++)
arr[i] = (String) b.get(i);
return arr;
}
private static void getTermNames(Expression x, Bag b, boolean varNames) {
if (x instanceof OpNode) {
OpNode o = (OpNode) x;
getTermNames(o.leftChild, b, varNames);
getTermNames(o.rightChild, b, varNames);
}
else if (x instanceof VarNode) {
if (varNames) {
VarNode v = (VarNode) x;
if (!b.contains(v.name))
b.add(v.name);
}
}
else if (x instanceof FuncNode) {
FuncNode f = (FuncNode) x;
if (!varNames) {
if (!b.contains(f.name))
b.add(f.name);
}
for (int i = 0; i < f.numChildren(); i++)
getTermNames(f.child(i), b, varNames);
}
}
/**
Returns a string that represents the expression tree rooted at this node.
*/
public String toString() {
StringBuffer sb = new StringBuffer();
toString(this, sb);
return sb.toString();
}
private static void toString(Expression x, StringBuffer sb) {
if (x instanceof OpNode) {
OpNode o = (OpNode) x;
sb.append("(");
toString(o.leftChild, sb);
sb.append(o.getSymbol());
toString(o.rightChild, sb);
sb.append(")");
}
else if (x instanceof TermNode) {
TermNode t = (TermNode) x;
if (t.getNegate()) {
sb.append("(");
sb.append("-");
}
sb.append(t.getName());
if (t instanceof FuncNode) {
FuncNode f = (FuncNode) t;
sb.append("(");
if (f.numChildren() > 0)
toString(f.child(0), sb);
for (int i = 1; i < f.numChildren(); i++) {
sb.append(", ");
toString(f.child(i), sb);
}
sb.append(")");
}
if (t.getNegate())
sb.append(")");
}
else if (x instanceof ValNode) {
sb.append(((ValNode) x).val);
}
}
}