bundles/org.simantics.utils.datastructures/src/org/simantics/utils/datastructures/persistent/ImmutableStack.java

   1 /*******************************************************************************
   2  * Copyright (c) 2007, 2010 Association for Decentralized Information Management
   3  * in Industry THTH ry.
   4  * All rights reserved. This program and the accompanying materials
   5  * are made available under the terms of the Eclipse Public License v1.0
   6  * which accompanies this distribution, and is available at
   7  * http://www.eclipse.org/legal/epl-v10.html
   8  *
   9  * Contributors:
  10  *     VTT Technical Research Centre of Finland - initial API and implementation
  11  *******************************************************************************/
  12 package org.simantics.utils.datastructures.persistent;
  13
  14 public abstract class ImmutableStack<T> {
  15
  16         private ImmutableStack() {
  17         }
  18
  19         private static class SingleStackNode<T> extends ImmutableStack<T> {
  20                 ImmutableStack<T> parent;
  21                 T value;
  22
  23                 public SingleStackNode(ImmutableStack<T> parent, T value) {
  24                         this.parent = parent;
  25                         this.value = value;
  26                 }
  27
  28                 @Override
  29                 public T get(int i) {
  30                         return i==0 ? value : parent.get(i-1);
  31                 }
  32         }
  33
  34         private static class MultiStackNode<T> extends ImmutableStack<T> {
  35                 ImmutableStack<T> parent;
  36                 T[] values;
  37
  38                 public MultiStackNode(ImmutableStack<T> parent, T[] values) {
  39                         this.parent = parent;
  40                         this.values = values;
  41                 }
  42
  43                 @Override
  44                 public T get(int i) {
  45                         return i<values.length ? values[i] : parent.get(i-values.length);
  46                 }
  47         }
  48
  49         private static class EmptyStack<T> extends ImmutableStack<T> {
  50
  51                 @Override
  52                 public T get(int i) {
  53                         throw new IllegalArgumentException("No such element in stack.");
  54                 }
  55
  56         }
  57
  58         @SuppressWarnings({ "rawtypes" })
  59         static final EmptyStack EMPTY = new EmptyStack();
  60
  61         public ImmutableStack<T> push(T value) {
  62                 return new SingleStackNode<T>(this, value);
  63         }
  64
  65         public ImmutableStack<T> push(T[] values) {
  66                 if(values.length > 1)
  67                         return new MultiStackNode<T>(this, values);
  68                 else if(values.length == 1)
  69                         return new SingleStackNode<T>(this, values[0]);
  70                 else
  71                         return this;
  72         }
  73
  74         public abstract T get(int i);
  75
  76         @SuppressWarnings("unchecked")
  77         public static <T> ImmutableStack<T> empty() {
  78                 return (ImmutableStack<T>)EMPTY;
  79         }
  80
  81         public static <T> ImmutableStack<T> of(T value) {
  82                 return new SingleStackNode<T>(null, value);
  83         }
  84
  85         @SuppressWarnings("unchecked")
  86         public static <T> ImmutableStack<T> of(T[] values) {
  87                 if(values.length > 1)
  88                         return new MultiStackNode<T>((ImmutableStack<T>)empty(), values);
  89                 else if(values.length == 1)
  90                         return new SingleStackNode<T>((ImmutableStack<T>)empty(), values[0]);
  91                 else
  92                         return empty();
  93         }
  94 }