Clean up code examples from Chapter 7 (Lambdas and Streams)

Author: jbloch

src/effectivejava/chapter6/item34/Operation.java

@@ -4,7 +4,7 @@
 
 import static java.util.stream.Collectors.toMap;
 
-// Enum type with constant-specific class bodies and data (Page 163-4)
+// Enum type with constant-specific class bodies and data (Pages 163-4)
 public enum Operation {
     PLUS("+") {
         public double apply(double x, double y) { return x + y; }

src/effectivejava/chapter7/item42/Operation.java

@@ -2,7 +2,7 @@
 
 import java.util.function.DoubleBinaryOperator;
 
-// Enum with function object fields & constant-specific behavior
+// Enum with function object fields & constant-specific behavior (Page 195)
 public enum Operation {
     PLUS  ("+", (x, y) -> x + y),
     MINUS ("-", (x, y) -> x - y),
@@ -22,4 +22,13 @@ public enum Operation {
     public double apply(double x, double y) {
         return op.applyAsDouble(x, y);
     }
+
+    // Main method from Item 34 (Page 163)
+    public static void main(String[] args) {
+        double x = Double.parseDouble(args[0]);
+        double y = Double.parseDouble(args[1]);
+        for (Operation op : Operation.values())
+            System.out.printf("%f %s %f = %f%n",
+                    x, op, y, op.apply(x, y));
+    }
 }

src/effectivejava/chapter7/item42/SortFourWays.java

@@ -8,11 +8,12 @@
 
 import static java.util.Comparator.comparingInt;
 
+// Sorting with function objects (Pages 193-4)
 public class SortFourWays {
     public static void main(String[] args) {
         List<String> words = Arrays.asList(args);
 
-        // Anonymous class instance as a function object - obsolete!
+        // Anonymous class instance as a function object - obsolete! (Page 193)
         Collections.sort(words, new Comparator<String>() {
             public int compare(String s1, String s2) {
                 return Integer.compare(s1.length(), s2.length());
@@ -21,16 +22,18 @@ public int compare(String s1, String s2) {
         System.out.println(words);
         Collections.shuffle(words);
 
-        // Lambda expression as function object (replaces anonymous class)
+        // Lambda expression as function object (replaces anonymous class) (Page 194)
         Collections.sort(words,
                 (s1, s2) -> Integer.compare(s1.length(), s2.length()));
         System.out.println(words);
         Collections.shuffle(words);
 
+        // Comparator construction method (with method reference) in place of lambda (Page 194)
         Collections.sort(words, comparingInt(String::length));
         System.out.println(words);
         Collections.shuffle(words);
 
+        // Default method List.sort in conjunction with comparator construction method (Page 194)
         words.sort(comparingInt(String::length));
         System.out.println(words);
     }

src/effectivejava/chapter7/item43/Freq.java

@@ -3,15 +3,19 @@
 import java.util.Map;
 import java.util.TreeMap;
 
-// p. 197
+// Frequency table implemented with map.merge, using lambda and method reference (Page 197)
 public class Freq {
     public static void main(String[] args) {
         Map<String, Integer> frequencyTable = new TreeMap<>();
-        for (String s : args) {
-//          map.merge(key, 1, (count, incr) -> count + incr);
-            frequencyTable.merge(s, 1, Integer::sum);
-        }
+        
+        for (String s : args)
+            frequencyTable.merge(s, 1, (count, incr) -> count + incr); // Lambda
+        System.out.println(frequencyTable);
 
+        frequencyTable.clear();
+        for (String s : args)
+            frequencyTable.merge(s, 1, Integer::sum); // Method reference
         System.out.println(frequencyTable);
+
     }
 }

src/effectivejava/chapter7/item45/Card.java

@@ -5,10 +5,11 @@
 import java.util.stream.Stream;
 import static java.util.stream.Collectors.*;
 
+// Generating the Cartesian product of two lists using iteration and streams (Page 209)
 public class Card {
     public enum Suit { SPADE, HEART, DIAMOND, CLUB }
     public enum Rank { ACE, DEUCE, THREE, FOUR, FIVE, SIX, SEVEN,
-        EIGHT, NINE, TEN, JACK, KING, QUEEN }
+                       EIGHT, NINE, TEN, JACK, QUEEN, KING }
 
     private final Suit suit;
     private final Rank rank;

src/effectivejava/chapter7/item45/CharStream.java

@@ -0,0 +1,14 @@
+package effectivejava.chapter7.item45;
+
+// Refrain from using streams to process char values (Page 206)
+public class CharStream {
+    public static void main(String[] args) {
+        // Does not produce the expected result
+        "Hello world!".chars().forEach(System.out::print);
+        System.out.println();
+
+        // Fixes the problem
+        "Hello world!".chars().forEach(x -> System.out.print((char) x));
+        System.out.println();
+    }
+}

src/effectivejava/chapter7/item45/MersennePrimes.java

@@ -5,7 +5,7 @@
 
 import static java.math.BigInteger.*;
 
-// P. 208
+// Generating the first twent Mersenne primes using streams (Page 208)
 public class MersennePrimes {
     static Stream<BigInteger> primes() {
         return Stream.iterate(TWO, BigInteger::nextProbablePrime);

src/effectivejava/chapter7/item45/anagrams/HybridAnagrams.java

@@ -9,7 +9,7 @@
 
 import static java.util.stream.Collectors.groupingBy;
 
-// Tasteful use of streams enhances clarity and conciseness
+// Tasteful use of streams enhances clarity and conciseness (Page 205)
 public class HybridAnagrams {
     public static void main(String[] args) throws IOException {
         Path dictionary = Paths.get(args[0]);

src/effectivejava/chapter7/item45/anagrams/IterativeAnagrams.java

@@ -4,7 +4,7 @@
 import java.io.IOException;
 import java.util.*;
 
-// Prints all large anagram groups in a dictionary iteratively
+// Prints all large anagram groups in a dictionary iteratively (Page 204)
 public class IterativeAnagrams {
     public static void main(String[] args) throws IOException {
         File dictionary = new File(args[0]);

src/effectivejava/chapter7/item45/anagrams/StreamAnagrams.java

@@ -8,7 +8,7 @@
 
 import static java.util.stream.Collectors.groupingBy;
 
-// Overuse of streams - don't do this! - (page 205)
+// Overuse of streams - don't do this! (page 205)
 public class StreamAnagrams {
     public static void main(String[] args) throws IOException {
         Path dictionary = Paths.get(args[0]);