Numeric streams, building streams, infinite streams

Author: raoulDoc

src/main/java/lambdasinaction/chap3/ExecuteAround.java

@@ -13,7 +13,7 @@ public static void main(String ...args) throws IOException{
 	}
 
 	public static String processFile(BufferedReaderProcessor p) throws IOException {
-		try(BufferedReader br = new BufferedReader(new FileReader("src/main/java/lambdasinaction/chap3/data.txt"))){
+		try(BufferedReader br = new BufferedReader(new FileReader("lambdasinaction/chap3/data.txt"))){
 			return p.process(br);
 		}
 
@@ -23,4 +23,4 @@ public interface BufferedReaderProcessor{
 		public String process(BufferedReader b) throws IOException;
 
 	}
-}
+}

src/main/java/lambdasinaction/chap4/BuildingStreams.java

@@ -0,0 +1,79 @@
+package lambdasinaction.chap4;
+
+import java.util.*;
+import java.util.function.IntSupplier;
+import java.util.stream.*;
+import static java.util.stream.Collectors.toList;
+import java.nio.charset.Charset;
+import java.nio.file.*;
+
+public class BuildingStreams {
+
+    public static void main(String...args) throws Exception{
+        
+        // Stream.of
+        Stream<String> stream = Stream.of("Java 8", "Lambdas", "In", "Action");
+        stream.map(String::toUpperCase).forEach(System.out::println);
+
+        // Stream.empty
+        Stream<String> emptyStream = Stream.empty();
+
+        // Arrays.stream
+        int[] numbers = {2, 3, 5, 7, 11, 13};
+        System.out.println(Arrays.stream(numbers).sum());
+
+        // Stream.iterate
+        Stream.iterate(0, n -> n + 2)
+              .limit(10)
+              .forEach(System.out::println);
+
+        // fibonnaci with iterate
+        Stream.iterate(new int[]{0, 1}, t -> new int[]{t[1],t[0] + t[1]})
+              .limit(10)
+              .forEach(t -> System.out.println("(" + t[0] + ", " + t[1] + ")"));
+        
+        Stream.iterate(new int[]{0, 1}, t -> new int[]{t[1],t[0] + t[1]})
+              .limit(10)
+              . map(t -> t[0])  
+              .forEach(System.out::println);
+
+        // random stream of doubles with Stream.generate
+        Stream.generate(Math::random)
+              .limit(10)
+              .forEach(System.out::println);
+ 
+        // stream of 1s with Stream.generate
+        IntStream.generate(() -> 1)
+                 .limit(5)
+                 .forEach(System.out::println);
+
+        IntStream.generate(new IntSupplier(){
+            public int getAsInt(){
+                return 2;
+            }
+        }).limit(5)
+          .forEach(System.out::println);
+   
+
+        IntSupplier fib = new IntSupplier(){
+                  private int previous = 0;
+                  private int current = 1;
+                  public int getAsInt(){
+                      int nextValue = this.previous + this.current;
+                      this.previous = this.current;
+                      this.current = nextValue;
+                      return this.previous;
+                  }
+              };
+         IntStream.generate(fib).limit(10).forEach(System.out::println);
+
+         long uniqueWords = Files.lines(Paths.get("lambdasinaction/chap4/data.txt"), Charset.defaultCharset())
+                                 .flatMap(line -> Arrays.stream(line.split(" ")))
+                                 .distinct()
+                                 .count();
+
+         System.out.println("There are " + uniqueWords + " unique words in data.txt");
+
+
+    }
+}

src/main/java/lambdasinaction/chap4/NumericStreams.java

@@ -0,0 +1,55 @@
+package lambdasinaction.chap4;
+import java.util.stream.*;
+import java.util.*;
+
+import static lambdasinaction.chap4.Dish.menu;
+
+public class NumericStreams{
+
+    public static void main(String...args){
+    
+        List<Integer> numbers = Arrays.asList(3,4,5,1,2);
+
+        Arrays.stream(numbers.toArray()).forEach(System.out::println);
+        int calories = menu.stream()
+                           .mapToInt(Dish::getCalories)
+                           .sum();
+        System.out.println("Number of calories:" + calories);
+
+
+        // max and OptionalInt
+        OptionalInt maxCalories = menu.stream()                                                      
+                                      .mapToInt(Dish::getCalories)
+                                      .max();
+
+        int max;
+        if(maxCalories.isPresent()){
+            max = maxCalories.getAsInt();
+        }
+        else {
+            // we can choose a default value
+            max = 1;
+        }
+        System.out.println(max);
+
+        // numeric ranges
+        IntStream evenNumbers = IntStream.rangeClosed(1, 100)
+                                 .filter(n -> n % 2 == 0);
+
+        System.out.println(evenNumbers.count());
+
+        Stream<int[]> pythagoreanTriples =
+               IntStream.rangeClosed(1, 100).boxed()
+                        .flatMap(a -> IntStream.rangeClosed(a, 100)
+                                               .filter(b -> Math.sqrt(a*a + b*b) % 1 == 0).boxed()
+                                               .map(b -> new int[]{a, b, (int) Math.sqrt(a * a + b * b)}));       
+
+        pythagoreanTriples.forEach(t -> System.out.println(t[0] + ", " + t[1] + ", " + t[2])); 
+
+    }
+   
+    public static boolean isPerfectSquare(int n){
+        return Math.sqrt(n) % 1 == 0;
+    }
+
+}

src/main/java/lambdasinaction/chap4/Reducing.java

@@ -20,5 +20,11 @@ public static void main(String...args){
 
         Optional<Integer> min = numbers.stream().reduce(Integer::min);
         min.ifPresent(v -> System.out.println(v));
+    
+
+        int calories = menu.stream()
+                           .map(Dish::getCalories)
+                           .reduce(0, Integer::sum);
+        System.out.println("Number of calories:" + calories);
     }
 }

src/main/java/lambdasinaction/chap4/StreamBasic.java

@@ -4,8 +4,7 @@
 import java.util.stream.*;
 import static java.util.stream.Collectors.toList;
 
-import lambdasinaction.chap5.Dish;
-import static lambdasinaction.chap5.Dish.menu;
+import static lambdasinaction.chap4.Dish.menu;
 
 public class StreamBasic {
 
@@ -17,4 +16,4 @@ public static void main(String...args){
                                  .collect(toList());              
         System.out.println(names);
     }
-}
+}

…main/java/lambdasinaction/chap3/data.txt …resources/lambdasinaction/chap3/data.txtsrc/main/java/lambdasinaction/chap3/data.txt renamed to src/main/resources/lambdasinaction/chap3/data.txt src/main/java/lambdasinaction/chap3/data.txt renamed to src/main/resources/lambdasinaction/chap3/data.txt

@@ -0,0 +1,2 @@
+The quick brown fox jumped over the lazy dog
+The lazy dog jumped over the quick brown fox