start lambda function section

src/section11/LambdaExpressions.java

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+package section11;
+
+import java.util.function.BiFunction;
+import java.util.function.Consumer;
+import java.util.function.Function;
+import java.util.function.Supplier;
+
+/**
+ * This class demonstrates the use of Lambda functions.
+ * Created by jzong on 3/14/18.
+ */
+public class LambdaExpressions {
+    public static void main(String[] argv) {
+        /* Defining lots of Lambda functions for use later */
+        // Function<T1, T2> takes in T1 and returns T2
+        // The following four functions are equivalent -- String to Integer parser
+        Function<String, Integer>
+                parseInt1 = s -> Integer.parseInt(s),
+                parseInt2 = s -> { return Integer.parseInt(s); },
+                parseInt3 = (String s) -> Integer.parseInt(s),
+                parseInt4 = (final String s) -> { return Integer.parseInt(s); };
+
+        // The following three functions are equivalent -- concating string arrays
+        Function<String[], String>
+                arrayConcat1 = ss -> String.join(",", ss),
+                arrayConcat2 = (String[] ss) -> String.join(",", ss),
+                arrayConcat3 = (String... ss) -> String.join(",", ss);
+
+        // BiFunction<T1, T2, T3> takes in (T1,T2) and returns T3
+        // The following two functions are equivalent -- returns 3-char substring starting from given index
+        BiFunction<String, Integer, String>
+                substr1 = (s, idx) -> s.substring(idx, Math.min(idx+3, s.length())),
+                substr2 = (s, idx) -> {
+                    int toIdx = Math.min(idx+3, s.length());
+                    return s.substring(idx, toIdx);
+                };
+
+        // Simple string concatenation
+        BiFunction<String, String, String>
+                concat = (s1, s2) -> s1 + s2;
+
+        // Supplier<T1> takes in nothing and returns T1
+        Supplier<String>
+                now = () -> new java.util.Date().toString();
+
+        // Consumer<T1> takes in T1 and returns void
+        Consumer<String>
+                display1 = s -> System.out.println(">>> " + s + " <<<"),
+                display2 = s -> { System.out.println(">>> " + s + " <<<"); };
+    }
+}