Expression.java

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package com.graphbuilder.math;

import com.graphbuilder.struc.Bag;

public abstract class Expression {

    protected Expression parent = null;

    public abstract double eval(VarMap v, FuncMap f);

    public boolean isDescendent(Expression x) {
        Expression y = this;

        while (y != null) {
            if (y == x)
                return true;
            y = y.parent;
        }

        return false;
    }

    public Expression getParent() {
        return parent;
    }

    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");
    }

    public String[] getVariableNames() {
        return getTermNames(true);
    }

    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);
        }
    }

    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);
        }
    }
}