Java Expressions and Assignments

public class NodeExpr extends Node { private NodeTerm term; private NodeAddop addop; private NodeExpr expr; public NodeExpr(NodeTerm term, NodeAddop addop, NodeExpr expr) { this.term=term; this.addop=addop; this.expr=expr; } public void append(NodeExpr expr) { if (this.expr==null) { this.addop=expr.addop; this.expr=expr; expr.addop=null; } else this.expr.append(expr); } public int eval(Environment env) throws EvalException { return expr==null ? term.eval(env) : addop.op(expr.eval(env),term.eval(env)); } }