# InstructionSequence.java

    /*
     * Licensed to the Apache Software Foundation (ASF) under one or more
     * contributor license agreements.  See the NOTICE file distributed with
     * this work for additional information regarding copyright ownership.
     * The ASF licenses this file to You under the Apache License, Version 2.0
     * (the "License"); you may not use this file except in compliance with
     * the License.  You may obtain a copy of the License at
     *
     *      http://www.apache.org/licenses/LICENSE-2.0
     *
     * Unless required by applicable law or agreed to in writing, software
     * distributed under the License is distributed on an "AS IS" BASIS,
     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     * See the License for the specific language governing permissions and
     * limitations under the License.
     */
    package org.apache.pdfbox.pdmodel.common.function.type4;

    import java.util.List;
    import java.util.Stack;

    /**
     * Represents an instruction sequence, a combination of values, operands and nested procedures.
     *
     */
    public class InstructionSequence
    {

        private final List<Object> instructions = new java.util.ArrayList<>();

        /**
         * Add a name (ex. an operator)
         * @param name the name
         */
        public void addName(String name)
        {
            this.instructions.add(name);
        }

        /**
         * Adds an int value.
         * @param value the value
         */
        public void addInteger(int value)
        {
            this.instructions.add(value);
        }

        /**
         * Adds a real value.
         * @param value the value
         */
        public void addReal(float value)
        {
            this.instructions.add(value);
        }

        /**
         * Adds a bool value.
         * @param value the value
         */
        public void addBoolean(boolean value)
        {
            this.instructions.add(value);
        }

        /**
         * Adds a proc (sub-sequence of instructions).
         * @param child the child proc
         */
        public void addProc(InstructionSequence child)
        {
            this.instructions.add(child);
        }

        /**
         * Executes the instruction sequence.
         * @param context the execution context
         */
        public void execute(ExecutionContext context)
        {
            Stack<Object> stack = context.getStack();
            for (Object o : instructions)
            {
                if (o instanceof String)
                {
                    String name = (String)o;
                    Operator cmd = context.getOperators().getOperator(name);
                    if (cmd != null)
                    {
                        cmd.execute(context);
                    }
                    else
                    {
                        throw new UnsupportedOperationException("Unknown operator or name: " + name);
                    }
                }
                else
                {
                    stack.push(o);
                }
            }

            //Handles top-level procs that simply need to be executed
            while (!stack.isEmpty() && stack.peek() instanceof InstructionSequence)
            {
                InstructionSequence nested = (InstructionSequence)stack.pop();
                nested.execute(context);
            }
        }

    }