Introduction to Scala

Updated examples

.gitignore

@@ -63,4 +63,6 @@ jmeter/src/main/resources/*-JMeter.csv
 **/tmp
 **/out-tsc
 **/nbproject/
-**/nb-configuration.xml
+**/nb-configuration.xml
+core-scala/.cache-main
+core-scala/.cache-tests

core-scala/pom.xml

@@ -47,7 +47,7 @@
     </build>
 
     <properties>
-        <scala.version>2.11.8</scala.version>
+        <scala.version>2.12.7</scala.version>
     </properties>
 </project>
 

core-scala/src/main/scala/com/baeldung/scala/ControlStructuresDemo.scala

@@ -0,0 +1,44 @@
+package com.baeldung.scala
+
+/**
+ * Sample code demonstrating the various control structured.
+ *
+ * @author Chandra Prakash
+ *
+ */
+object ControlStructuresDemo {
+  def gcd(x : Int, y : Int) : Int = {
+    if (y == 0) x else gcd(y, x % y)
+  }
+
+  def gcdIter(x : Int, y : Int) : Int = {
+    var a = x
+    var b = y
+    while (b > 0) {
+      a = a % b
+      val t = a
+      a = b
+      b = t
+    }
+    a
+  }
+
+  def rangeSum(a : Int, b : Int) = {
+    var sum = 0;
+    for (i <- a to b) {
+      sum += i
+    }
+    sum
+  }
+
+  def factorial(a : Int) : Int = {
+    var result = 1;
+    var i = 1;
+    do {
+      result *= i
+      i = i + 1
+    } while (i <= a)
+    result
+  }
+
+}

core-scala/src/main/scala/com/baeldung/scala/Employee.scala

@@ -1,10 +1,27 @@
 package com.baeldung.scala
 
-class Employee(val name: String, var salary: Int, annualIncrement: Int = 20) extends AnyRef {
+/**
+ * Sample Code demonstrating a class.
+ *
+ * @author Chandra Prakash
+ *
+ */
+class Employee(val name : String,
+               var salary : Int,
+               annualIncrement : Int = 20) {
 
-    def incrementSalary(): Unit = {
-        salary += annualIncrement
-    }
+  def incrementSalary() : Unit = {
+    salary += annualIncrement
+  }
+
+  override def toString =
+    s"Employee(name=$name, salary=$salary)"
+}
+
+/**
+ * A Trait which will make the toString return upper case value.
+ */
+trait UpperCasePrinter {
+  override def toString = super.toString toUpperCase
+}
 
-    override def toString = s"Employee(name=$name, salary=$salary)"
-}

core-scala/src/main/scala/com/baeldung/scala/HelloWorld.scala

@@ -1,6 +1,6 @@
 package com.baeldung.scala
 
 object HelloWorld extends App {
-    println("Hello World!")
-    args foreach println
+  println("Hello World!")
+  args foreach println
 }

core-scala/src/main/scala/com/baeldung/scala/HigherOrderFunctions.scala

@@ -1,14 +1,27 @@
-
-
 package com.baeldung.scala
 
+/**
+ * Sample higher order functions.
+ *
+ * @author Chandra Prakash
+ *
+ */
 object HigherOrderFunctions {
 
-    def mapReduce(r: (Int, Int) => Int, i: Int, m: Int => Int, a: Int, b: Int) = {
-        def iter(a: Int, result: Int): Int = {
-            if (a > b) result
-            else iter(a + 1, r(m(a), result))
-        }
-        iter(a, i)
+  def mapReduce(r : (Int, Int) => Int,
+                i : Int,
+                m : Int => Int,
+                a : Int, b : Int) = {
+    def iter(a : Int, result : Int) : Int = {
+      if (a > b) result
+      else iter(a + 1, r(m(a), result))
+    }
+    iter(a, i)
+  }
+
+  def whileLoop(condition : => Boolean)(body : => Unit) : Unit =
+    if (condition) {
+      body
+      whileLoop(condition)(body)
     }
 }

core-scala/src/main/scala/com/baeldung/scala/IntSet.scala

@@ -0,0 +1,34 @@
+package com.baeldung.scala
+
+/**
+ * An abstract class for set of integers and its implementation.
+ *
+ * @author Chandra Prakash
+ *
+ */
+abstract class IntSet {
+  // add an element to the set
+  def incl(x : Int) : IntSet
+
+  // whether an element belongs to the set
+  def contains(x : Int) : Boolean
+}
+
+class EmptyIntSet extends IntSet {
+
+  def contains(x : Int) : Boolean = false
+
+  def incl(x : Int) =
+    new NonEmptyIntSet(x, this)
+}
+
+class NonEmptyIntSet(val head : Int, val tail : IntSet)
+  extends IntSet {
+
+  def contains(x : Int) : Boolean =
+    head == x || (tail contains x)
+
+  def incl(x : Int) : IntSet =
+    if (this contains x) this
+    else new NonEmptyIntSet(x, this)
+}

core-scala/src/main/scala/com/baeldung/scala/Utils.scala

@@ -1,66 +1,33 @@
 package com.baeldung.scala
 
+/**
+ * Some utility methods.
+ *
+ * @author Chandra Prakash
+ *
+ */
 object Utils {
-    def average(x: Double, y: Double) = (x + y) / 2
+  def average(x : Double, y : Double) = (x + y) / 2
 
-    def gcd(x: Int, y: Int): Int = {
-        if (y == 0) x else gcd(y, x % y)
+  def randomLessThan(d : Double) = {
+    var random = 0d
+    do {
+      random = Math.random()
+    } while (random >= d)
+    random
+  }
+
+  def power(x : Int, y : Int) : Int = {
+    def powNested(i : Int, accumulator : Int) : Int = {
+      if (i <= 0) accumulator
+      else powNested(i - 1, x * accumulator)
     }
+    powNested(y, 1)
+  }
 
-    def gcdIter(x: Int, y: Int): Int = {
-        var a = x
-        var b = y
-        while (b > 0) {
-            a = a % b
-            val t = a
-            a = b
-            b = t
-        }
-        return a
-    }
-
-    def rangeSum(a: Int, b: Int) = {
-        var sum = 0;
-        for (i <- a to b) {
-            sum += i
-        }
-        sum
-    }
-
-    def factorial(a: Int): Int = {
-        var result = 1;
-        var i = a;
-        do {
-            result *= i
-            i = i - 1
-        } while (i > 0)
-        result
-    }
-
-    def randomLessThan(d: Double) = {
-        var random = 0d
-        do {
-            random = Math.random()
-        } while (random >= d)
-        random
-    }
-
-    def whileLoop(condition: => Boolean)(body: => Unit): Unit =
-        if (condition) {
-            body
-            whileLoop(condition)(body)
-        }
-
-    def power(x: Int, y: Int): Int = {
-        def powNested(i: Int, accumulator: Int): Int = {
-            if (i <= 0) accumulator
-            else powNested(i - 1, x * accumulator)
-        }
-        powNested(y, 1)
-    }
-
-    def fibonacci(n: Int): Int = n match {
-        case 0 | 1      => 1
-        case x if x > 1 => fibonacci(x - 1) + fibonacci(x - 2)
-    }
+  def fibonacci(n : Int) : Int = n match {
+    case 0 | 1 => 1
+    case x if x > 1 =>
+      fibonacci(x - 1) + fibonacci(x - 2)
+  }
 }

core-scala/src/test/scala/com/baeldung/scala/ControlStructuresDemoUnitTest.scala

@@ -0,0 +1,33 @@
+package com.baeldung.scala
+
+import com.baeldung.scala.ControlStructuresDemo._
+import org.junit.Test
+import org.junit.Assert.assertEquals
+
+class ControlStructuresDemoUnitTest {
+  @Test
+  def givenTwoIntegers_whenGcdCalled_thenCorrectValueReturned = {
+    assertEquals(3, gcd(15, 27))
+  }
+
+  @Test
+  def givenTwoIntegers_whenGcdIterCalled_thenCorrectValueReturned = {
+    assertEquals(3, gcdIter(15, 27))
+  }
+
+  @Test
+  def givenTwoIntegers_whenRangeSumcalled_thenCorrectValueReturned = {
+    assertEquals(55, rangeSum(1, 10))
+  }
+
+  @Test
+  def givenPositiveInteger_whenFactorialInvoked_thenCorrectValueReturned = {
+    assertEquals(720, factorial(6))
+  }
+
+  @Test
+  def whenFactorialOf0Invoked_then1Returned = {
+    assertEquals(1, factorial(0))
+  }
+
+}

core-scala/src/test/scala/com/baeldung/scala/EmployeeUnitTest.scala

@@ -1,22 +1,30 @@
 package com.baeldung.scala
 
+import org.junit.Assert.assertEquals
 import org.junit.Test
-import org.junit.Assert._
 
 class EmployeeUnitTest {
 
-    @Test
-    def whenEmployeeSalaryIncremented_thenCorrectSalary() = {
-        val employee = new Employee("John Doe", 1000);
-        employee.incrementSalary();
-        assertEquals(1020, employee.salary);
-    }
+  @Test
+  def whenEmployeeSalaryIncremented_thenCorrectSalary = {
+    val employee = new Employee("John Doe", 1000)
+    employee.incrementSalary()
+    assertEquals(1020, employee.salary)
+  }
+
+  @Test
+  def givenEmployee_whenToStringCalled_thenCorrectStringReturned = {
+    val employee = new Employee("John Doe", 1000)
+    assertEquals("Employee(name=John Doe, salary=1000)", employee.toString)
+  }
+
+  @Test
+  def givenEmployeeWithTrait_whenToStringCalled_thenCorrectStringReturned = {
+    val employee =
+      new Employee("John Doe", 1000) with UpperCasePrinter
+    assertEquals("EMPLOYEE(NAME=JOHN DOE, SALARY=1000)", employee.toString)
+  }
 
-    @Test
-    def givenEmployee_whenToStringCalled_thenCorrectStringReturned() = {
-        val employee = new Employee("John Doe", 1000);
-        assertEquals("Employee(name=John Doe, salary=1000)", employee.toString);
-    }
 }
 
 

core-scala/src/test/scala/com/baeldung/scala/HigherOrderFunctionsUnitTest.scala

@@ -1,44 +1,49 @@
 package com.baeldung.scala
 
+import org.junit.Assert.assertEquals
 import org.junit.Test
-import org.junit.Assert._
-import HigherOrderFunctions._
+
+import HigherOrderFunctions.mapReduce
 
 class HigherOrderFunctionsUnitTest {
 
-    @Test
-    def whenCalledWithSumAndSquareFunctions_thenCorrectValueReturned = {
-        def square(x: Int) = x * x
+  @Test
+  def whenCalledWithSumAndSquareFunctions_thenCorrectValueReturned = {
+    def square(x : Int) = x * x
 
-        def sum(x: Int, y: Int) = x + y
+    def sum(x : Int, y : Int) = x + y
 
-        def sumSquares(a: Int, b: Int) =
-            mapReduce(sum, 0, square, a, b)
+    def sumSquares(a : Int, b : Int) =
+      mapReduce(sum, 0, square, a, b)
 
-        val n = 10
-        val expected = n * (n + 1) * (2 * n + 1) / 6
-        assertEquals(expected, sumSquares(1, n));
-    }
+    assertEquals(385, sumSquares(1, 10))
+  }
 
-    @Test
-    def whenComputingSumOfSquaresWithAnonymousFunctions_thenCorrectValueReturned = {
-        def sumSquares(a: Int, b: Int) =
-            mapReduce((x, y) => x + y, 0, x => x * x, a, b)
+  @Test
+  def whenComputingSumOfSquaresWithAnonymousFunctions_thenCorrectValueReturned = {
+    def sumSquares(a : Int, b : Int) =
+      mapReduce((x, y) => x + y, 0, x => x * x, a, b)
 
-        val n = 10
-        val expected = n * (n + 1) * (2 * n + 1) / 6
-        assertEquals(expected, sumSquares(1, n));
-    }
+    assertEquals(385, sumSquares(1, 10))
+  }
 
-    @Test
-    def givenCurriedFunctions_whenInvoked_thenCorrectValueReturned = {
-        def sum(f: Int => Int)(a: Int, b: Int): Int =
-            if (a > b) 0 else f(a) + sum(f)(a + 1, b)
+  @Test
+  def givenCurriedFunctions_whenInvoked_thenCorrectValueReturned = {
+    // a curried function
+    def sum(f : Int => Int)(a : Int,
+                            b : Int) : Int =
+      if (a > b) 0 else f(a) + sum(f)(a + 1, b)
 
-        def mod(n: Int)(x: Int) = x % n
+    // another curried function
+    def mod(n : Int)(x : Int) = x % n
 
-        def sumMod5 = sum(mod(5)) _
-        
-        assertEquals(10, sumMod5(6,10));
-    }
+    // application of a curried function
+    assertEquals(1, mod(5)(6))
+
+    // partial application of curried function
+    // trailing underscore is required to make function type explicit
+    val sumMod5 = sum(mod(5)) _
+
+    assertEquals(10, sumMod5(6, 10))
+  }
 }

core-scala/src/test/scala/com/baeldung/scala/IntSetUnitTest.scala

@@ -0,0 +1,23 @@
+package com.baeldung.scala
+
+import scala.Range
+
+import org.junit.Assert.assertFalse
+import org.junit.Test
+
+class IntSetUnitTest {
+
+  @Test
+  def givenSetof1To10_whenContains11Called_thenFalse = {
+
+    // Set up a set containing integers 1 to 10.
+    val set1To10 =
+      Range(1, 10)
+        .foldLeft(new EmptyIntSet() : IntSet) {
+          (x, y) => x incl y
+        }
+
+    assertFalse(set1To10 contains 11)
+  }
+
+}

core-scala/src/test/scala/com/baeldung/scala/UtilsUnitTest.scala

@@ -1,50 +1,37 @@
 package com.baeldung.scala
 
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertTrue
 import org.junit.Test
-import Utils._
-import org.junit.Assert._
+
+import Utils.average
+import Utils.fibonacci
+import Utils.power
+import Utils.randomLessThan
 
 class UtilsUnitTest {
 
-    @Test
-    def whenAverageCalled_thenCorrectValueReturned() = {
-        val average = Utils.average(10, 20)
-        assertEquals(15.0, average, 1e-5)
-    }
+  @Test
+  def whenAverageCalled_thenCorrectValueReturned() = {
+    assertEquals(15.0, average(10, 20), 1e-5)
+  }
 
-    @Test
-    def givenTwoIntegers_whenGcdCalled_thenCorrectValueReturned = {
-        assertEquals(3, Utils.gcd(15, 27))
-    }
+  @Test
+  def whenRandomLessThanInvokedWithANumber_thenARandomLessThanItReturned = {
+    val d = 0.1
+    assertTrue(randomLessThan(d) < d)
+  }
 
-    @Test
-    def givenTwoIntegers_whenGcdIterCalled_thenCorrectValueReturned = {
-        assertEquals(3, Utils.gcdIter(15, 27))
-    }
+  @Test
+  def whenPowerInvokedWith2And3_then8Returned = {
+    assertEquals(8, power(2, 3))
+  }
 
-    @Test
-    def givenTwoIntegers_whenRangeSumcalled_thenCorrectValueReturned = {
-        assertEquals(55, Utils.rangeSum(1, 10))
-    }
-
-    @Test
-    def givenPositiveInteger_whenFactorialInvoked_thenCorrectValueReturned = {
-        assertEquals(720, Utils.factorial(6))
-    }
-
-    @Test
-    def whenRandomLessThanInvokedWithANumber_thenARandomLessThanItReturned = {
-        val d = 0.1
-        assertTrue(Utils.randomLessThan(d) < d)
-    }
-
-    @Test
-    def whenPowerInvokedWith2And3_then8Returned = {
-        assertEquals(8, power(2, 3))
-    }
-
-    @Test
-    def whenFibonacciCalled_thenCorrectValueReturned = {
-        assertEquals(34, fibonacci(8))
-    }
+  @Test
+  def whenFibonacciCalled_thenCorrectValueReturned = {
+    assertEquals(1, fibonacci(0))
+    assertEquals(1, fibonacci(1))
+    assertEquals(fibonacci(6),
+      fibonacci(4) + fibonacci(5))
+  }
 }