{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# 1. Interfaces"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Interfaces are used to define a set of methods that a class must have in order to be a valid type of that class.\n",
    "\n",
    "1. define the `interface`\n",
    "2. define a class that `extends` that interface\n",
    "\n",
    "First we define an interface:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "|  Added interface Human\n",
      "\n"
     ]
    }
   ],
   "source": [
    "interface Human {\n",
    "    public abstract double age();\n",
    "}"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "What can we do with it?"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Human is sorta like a type/class... we spell it with a capital letter...."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stderr",
     "output_type": "stream",
     "text": [
      "|  Error:\n",
      "|  Human is abstract; cannot be instantiated\n",
      "|  new Human()\n",
      "|  ^---------^\n",
      "\n"
     ]
    }
   ],
   "source": [
    "new Human()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "No, you can create an instance of an interface. But you can create a class that implements it:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stderr",
     "output_type": "stream",
     "text": [
      "|  Error:\n",
      "|  Student is not abstract and does not override abstract method age() in Human\n",
      "|  class Student implements Human {\n",
      "|  ^-------------------------------...\n",
      "\n"
     ]
    }
   ],
   "source": [
    "class Student implements Human {\n",
    "\n",
    "}"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "...but only if you satisfy the requirements of the interface:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "|  Added class Student\n",
      "\n"
     ]
    }
   ],
   "source": [
    "class Student implements Human {\n",
    "    public double age() {\n",
    "        return 19.0;\n",
    "    }\n",
    "}"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Now, you can use the class as you would normally:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "|  Added variable student of type Student with initial value Student@4ca8195f\n",
      "\n"
     ]
    }
   ],
   "source": [
    "Student student = new Student();"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "|  Expression value is: 19.0\n",
      "|    assigned to temporary variable $4 of type double\n",
      "\n"
     ]
    },
    {
     "data": {
      "text/plain": [
       "19.0"
      ]
     },
     "execution_count": 6,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "student.age();"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "In addition, you can \"cast\" a class as an interface. If you do that, you can only use methods that exist in Human:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "|  Added variable human of type Human with initial value Student@4ca8195f\n",
      "\n"
     ]
    }
   ],
   "source": [
    "Human human = student;"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "You can also cast it explicitly like: `((Human)student)`"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "|  Expression value is: 19.0\n",
      "|    assigned to temporary variable $6 of type double\n",
      "\n"
     ]
    },
    {
     "data": {
      "text/plain": [
       "19.0"
      ]
     },
     "execution_count": 8,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "human.age()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "|  Replaced class Student\n",
      "|    Update replaced variable student, reset to null\n",
      "|    Update overwrote class Student\n",
      "\n"
     ]
    }
   ],
   "source": [
    "class Student implements Human {\n",
    "    public double age() {\n",
    "        return 19.0;\n",
    "    }\n",
    "    public boolean in_cs206() {\n",
    "        return true;\n",
    "    }\n",
    "}"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "|  Modified variable student of type Student with initial value Student@d70c109\n",
      "\n"
     ]
    }
   ],
   "source": [
    "Student student = new Student();"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "|  Expression value is: true\n",
      "|    assigned to temporary variable $9 of type boolean\n",
      "\n"
     ]
    },
    {
     "data": {
      "text/plain": [
       "true"
      ]
     },
     "execution_count": 12,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "student.in_cs206();"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "|  Added class Teacher\n",
      "\n"
     ]
    }
   ],
   "source": [
    "class Teacher implements Human {\n",
    "    public double age() {\n",
    "        return 52.0;\n",
    "    }\n",
    "    public boolean has_tenure() {\n",
    "        return true;\n",
    "    }\n",
    "}"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "|  Added variable teacher of type Teacher with initial value Teacher@2d6a9952\n",
      "\n"
     ]
    }
   ],
   "source": [
    "Teacher teacher = new Teacher();"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 16,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "|  Expression value is: 52.0\n",
      "|    assigned to temporary variable $12 of type double\n",
      "\n"
     ]
    },
    {
     "data": {
      "text/plain": [
       "52.0"
      ]
     },
     "execution_count": 16,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "teacher.age()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 17,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "|  Added variable alist of type ArrayList<Human> with initial value []\n",
      "\n"
     ]
    }
   ],
   "source": [
    "ArrayList<Human> alist = new ArrayList<Human>();"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 18,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "|  Expression value is: true\n",
      "|    assigned to temporary variable $14 of type boolean\n",
      "\n"
     ]
    },
    {
     "data": {
      "text/plain": [
       "true"
      ]
     },
     "execution_count": 18,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "alist.add(teacher);"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 19,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "|  Expression value is: true\n",
      "|    assigned to temporary variable $15 of type boolean\n",
      "\n"
     ]
    },
    {
     "data": {
      "text/plain": [
       "true"
      ]
     },
     "execution_count": 19,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "alist.add(student);"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 20,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Age: 52.0\n",
      "Age: 19.0\n",
      "\n"
     ]
    }
   ],
   "source": [
    "for (Human human: alist) {\n",
    "    printf(\"Age: %s\\n\", human.age());\n",
    "}"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 21,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "|  Modified variable human of type Human with initial value Teacher@2d6a9952\n",
      "\n"
     ]
    }
   ],
   "source": [
    "Human human = teacher;"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 23,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "|  Expression value is: true\n",
      "|    assigned to temporary variable $18 of type boolean\n",
      "\n"
     ]
    },
    {
     "data": {
      "text/plain": [
       "true"
      ]
     },
     "execution_count": 23,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "teacher.has_tenure()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "*See page 6 of your textbook for more information.*"
   ]
  }
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