Adding snippets and testing tools

.github/tools/pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>tools</artifactId>
+    <version>1.0.0</version>
+    <groupId>dev.playground</groupId>
+
+    <properties>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+        <maven.compiler.source>21</maven.compiler.source>
+        <maven.compiler.target>21</maven.compiler.target>
+        <mainClass>dev.playground.tools.IndexJson</mainClass>
+        <junit.version>5.9.2</junit.version>
+    </properties>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter</artifactId>
+            <version>${junit.version}</version>
+            <scope>compile</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-engine</artifactId>
+            <version>${junit.version}</version>
+            <scope>compile</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-api</artifactId>
+            <version>${junit.version}</version>
+            <scope>compile</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <artifactId>maven-jar-plugin</artifactId>
+                <version>3.0.2</version>
+                <configuration>
+                    <archive>
+                        <manifest>
+                            <addClasspath>true</addClasspath>
+                            <mainClass>${mainClass}</mainClass>
+                        </manifest>
+                    </archive>
+                </configuration>
+            </plugin>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>3.11.0</version>
+                <configuration>
+                    <source>${maven.compiler.source}</source>
+                    <target>${maven.compiler.target}</target>
+                </configuration>
+            </plugin>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-surefire-plugin</artifactId>
+                <version>2.22.1</version>
+            </plugin>
+        </plugins>
+    </build>
+</project>

.github/tools/src/main/java/dev/playground/tools/IndexJson.java

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+package dev.playground.tools;
+
+import java.io.File;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.stream.Collectors;
+
+public class IndexJson {
+
+    static final String rawGithubCDNPrefix = "https://raw.githubusercontent.com/java/playground-snippets/main/";
+
+    public static void main(String[] args) throws IOException {
+        if (args.length < 1) {
+            System.err.println("USAGE:\n\t[program] <path-to-snippets-folder>");
+            System.exit(1);
+        }
+        var strPath = args[0];
+        var path = Path.of(strPath);
+        if (!path.toFile().exists()) {
+            System.err.printf("Directory %s does not exist!\nUSAGE:\n\t[program] <path-to-snippets-folder>\n", path);
+            System.exit(1);
+        }
+
+        String result;
+        try(var walker = Files.walk(path)) {
+            result = walker.filter(f -> !Files.isDirectory(f)).map(key -> {
+                var strKey = key.toString().replace(strPath + "/", "");
+                var strValue = rawGithubCDNPrefix + strKey;
+
+                return String.format("\t\"%s\": \"%s\"", strKey, strValue);
+            }).collect(Collectors.joining(",\n"));
+        }
+        var indexJsonContent = String.format("{\n%s\n}", result);
+        var indexJsonFilePath = Path.of(strPath, "index.json");
+        System.out.println(indexJsonFilePath);
+        Files.deleteIfExists(indexJsonFilePath);
+        indexJsonFilePath.toFile().createNewFile();
+
+        Files.writeString(indexJsonFilePath, indexJsonContent);
+        System.out.println(indexJsonContent);
+    }
+}

.github/tools/src/main/resources/README.md

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+# DISCLAIMER
+
+
+[snippets](snippets) is a symlink to a [root folder](../../../../../snippets).

.github/tools/src/main/resources/snippets/hello-world.snippet

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+var name = "Duke";
+
+System.out.println("Hello, " + name);

.github/tools/src/main/resources/snippets/index.json

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+{
+	"misc/simple-collection.snippet": "https://raw.githubusercontent.com/java/playground-snippets/main/misc/simple-collection.snippet",
+	"misc/func-interface.snippet": "https://raw.githubusercontent.com/java/playground-snippets/main/misc/func-interface.snippet",
+	"misc/functions-chaining.snippet": "https://raw.githubusercontent.com/java/playground-snippets/main/misc/functions-chaining.snippet",
+	"records/composing.snippet": "https://raw.githubusercontent.com/java/playground-snippets/main/records/composing.snippet",
+	"records/simple.snippet": "https://raw.githubusercontent.com/java/playground-snippets/main/records/simple.snippet",
+	"records/method-overriding.snippet": "https://raw.githubusercontent.com/java/playground-snippets/main/records/method-overriding.snippet",
+	"streams/filtering.snippet": "https://raw.githubusercontent.com/java/playground-snippets/main/streams/filtering.snippet",
+	"streams/stream-to-list.snippet": "https://raw.githubusercontent.com/java/playground-snippets/main/streams/stream-to-list.snippet",
+	"streams/text-block-to-stream.snippet": "https://raw.githubusercontent.com/java/playground-snippets/main/streams/text-block-to-stream.snippet",
+	"textblocks/formatting.snippet": "https://raw.githubusercontent.com/java/playground-snippets/main/textblocks/formatting.snippet",
+	"textblocks/simple.snippet": "https://raw.githubusercontent.com/java/playground-snippets/main/textblocks/simple.snippet",
+	"textblocks/record.snippet": "https://raw.githubusercontent.com/java/playground-snippets/main/textblocks/record.snippet",
+	"hello-world.snippet": "https://raw.githubusercontent.com/java/playground-snippets/main/hello-world.snippet",
+	"switch/expression.snippet": "https://raw.githubusercontent.com/java/playground-snippets/main/switch/expression.snippet",
+	"switch/pattern-matching.snippet": "https://raw.githubusercontent.com/java/playground-snippets/main/switch/pattern-matching.snippet",
+	"switch/statement.snippet": "https://raw.githubusercontent.com/java/playground-snippets/main/switch/statement.snippet",
+	"pattern-matching/record.snippet": "https://raw.githubusercontent.com/java/playground-snippets/main/pattern-matching/record.snippet",
+	"pattern-matching/switch.snippet": "https://raw.githubusercontent.com/java/playground-snippets/main/pattern-matching/switch.snippet"
+}

.github/tools/src/main/resources/snippets/misc/func-interface.snippet

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+@FunctionalInterface
+interface MyFunctionalInterface {
+    public int incrementByTwo(int a);
+}
+
+MyFunctionalInterface f = (num) -> num + 2;
+var result = f.incrementByTwo(40);
+
+System.out.println(result);

.github/tools/src/main/resources/snippets/misc/functions-chaining.snippet

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+var strings = Arrays.asList("one", null, "three", "", "five", "six");
+
+Function<String, String> handleNull = s -> s == null ? "": s;
+Function<String, Integer> length = s -> s.length();
+Function<String, Integer> handleNullThenLength = handleNull.andThen(length);
+
+for (String string : strings) {
+    System.out.println(string + " -> length = " + handleNullThenLength.apply(string));
+}

.github/tools/src/main/resources/snippets/misc/simple-collection.snippet

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+Collection<String> numbers = new ArrayList<>();
+numbers.add("one");
+numbers.add("two");
+numbers.add("three");
+numbers.remove("two");
+System.out.println(numbers);

.github/tools/src/main/resources/snippets/pattern-matching/record.snippet

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+record Point(int x, int y) {
+    public boolean equals(Object other) {
+        return other instanceof Point otherPoint &&
+                this.x == otherPoint.x && this.y == otherPoint.y;
+    }
+}
+
+Point p1 = new Point(0, 0);
+Point p2 = new Point(1, 1);
+Point p3 = new Point(0, 0);
+System.out.println("p1 equals object? " + p1.equals(new Object()));
+System.out.println("p1 equals p2? " + p1.equals(p2));
+System.out.println("p1 equals p3? " + p1.equals(p3));
+System.out.println("p2 equals p3? " + p2.equals(p3));

.github/tools/src/main/resources/snippets/pattern-matching/switch.snippet

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+record Point(int x, int y) {}
+
+record Circle(Point center, int radius) {
+    public Circle {
+        if (radius < 0) throw new IllegalArgumentException("Radius cant be null");
+    }
+}
+
+ToDoubleFunction<Object> surface = object ->
+    switch(object) {
+        case null -> throw new AssertionError("Object is null");
+        case Circle(Point p, int radius) when radius == 0 -> 0d;
+        case Circle(Point p, int radius) -> Math.PI*radius*radius;
+        case Object notACircle -> throw new AssertionError("Object is not a circle");
+    };
+
+Circle c1 = new Circle(new Point(0, 0), 0);
+Circle c2 = new Circle(new Point(1, 1), 1);
+
+System.out.println("Surface of " + c1 + " = " + surface.applyAsDouble(c1));
+System.out.println("Surface of " + c2 + " = " + surface.applyAsDouble(c2));
+surface.applyAsDouble(null);
+surface.applyAsDouble("Not a circle!");

.github/tools/src/main/resources/snippets/records/composing.snippet

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+record Population(int population) {}
+record City(String name, Population population) {
+    // static methods are allowed in records
+    public static City of(String name, int p) {
+        var population = new Population(p);
+        return new City(name, population);
+    }
+}
+
+var paris = City.of("Paris", 2_161);
+System.out.println(paris);

.github/tools/src/main/resources/snippets/records/method-overriding.snippet

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+record City(String name) {
+
+    public boolean equals(Object other) {
+        return other instanceof City(String name) &&
+                this.name.equalsIgnoreCase(name);
+    }
+
+    public int hashCode() {
+        return name != null ? name.toUpperCase().hashCode() : 0;
+    }
+}
+
+var paris1 = new City("Paris");
+var paris2 = new City("paris");
+var paris3 = new City("PARIS");
+System.out.println("1 == 2 ? " + paris1.equals(paris2));
+System.out.println("2 == 3 ? " + paris2.equals(paris3));
+System.out.println("1 == 3 ? " + paris1.equals(paris3));

.github/tools/src/main/resources/snippets/records/simple.snippet

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+record Player(String last, String first, int level) {}
+var jane = new Player("Doe", "Jane", 42);
+System.out.println(jane);

.github/tools/src/main/resources/snippets/streams/filtering.snippet

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+List<String> cities =
+            Arrays.asList("Shenzhen", "Brussels", "Taipei", "Buenos Aires", "Sydney", "Bristol");
+
+cities.stream()
+      .filter(s -> s.startsWith("B"))
+      .map(String::toUpperCase)
+      .sorted()
+      .forEach(System.out::println);

.github/tools/src/main/resources/snippets/streams/stream-to-list.snippet

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+Stream<String> stream = Stream.of("Shenzhen", "Brussels", "Taipei", "Buenos Aires", "Sydney", "Bristol");
+
+List<String> cities = stream.sorted().collect(Collectors.toList());
+
+System.out.println(cities);

.github/tools/src/main/resources/snippets/streams/text-block-to-stream.snippet

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+var cities = """
+      San Francisco
+      Casablanca
+      Antwerp
+      New Delhi
+      Osaka
+""";
+
+Stream<String> lines = cities.lines();
+
+System.out.println(lines.toList());

.github/tools/src/main/resources/snippets/switch/expression.snippet

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+enum Day { SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY; }
+
+Day day = Day.SUNDAY;
+int numLetters = switch (day) {
+    case MONDAY, FRIDAY, SUNDAY -> 6;
+    case TUESDAY                -> 7;
+    case THURSDAY, SATURDAY     -> 8;
+    case WEDNESDAY              -> 9;
+};
+
+System.out.println(numLetters);

.github/tools/src/main/resources/snippets/switch/pattern-matching.snippet

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+var result = switch ("Lorem Ipsum") {
+        case null         -> "Oops";
+        case "Foo", "Bar" -> "Great";
+        default           -> "Ok!";
+};
+System.out.println(result);

.github/tools/src/main/resources/snippets/switch/statement.snippet

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+enum Day { SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY; }
+var numberOfChar = 0;
+
+switch(Day.MONDAY) {
+    case MONDAY: case FRIDAY: case SUNDAY:
+        numberOfChar = 6;
+        break;
+    case TUESDAY:
+        numberOfChar = 7;
+        break;
+    case WEDNESDAY:
+        numberOfChar = 9;
+        break;
+    case THURSDAY: case SATURDAY:
+        numberOfChar = 8;
+        break;
+    default:
+        throw new IllegalArgumentException();
+}
+
+System.out.println(numberOfChar);

.github/tools/src/main/resources/snippets/textblocks/formatting.snippet

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+var message = """
+        {"name" : "%s", "language" : "Java"}
+""";
+System.out.println(message.formatted("Duke"));

.github/tools/src/main/resources/snippets/textblocks/record.snippet

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+record City(String name, int population) {
+
+    public static City of(String line) {
+        int indexOfLastSpace = line.lastIndexOf(' ');
+        var name = line.substring(0, indexOfLastSpace);
+        var population = Integer.parseInt(line.substring(indexOfLastSpace + 1));
+        return new City(name, population);
+    }
+}
+
+String cities = """
+    New York 8343
+    London 8982
+    Paris 2161
+    Bangaluru 8474
+    Singapore 5454
+    Tokyo 13960
+    """;
+
+var cityList = cities.lines().map(City::of).toList();
+cityList.forEach(System.out::println);

.github/tools/src/main/resources/snippets/textblocks/simple.snippet

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+String cities = """
+    New York   \s
+    Paris      \s
+    Bangalore  \s
+    Singapore  \s
+    Tokyo      \s
+    """;
+
+cities.lines().map(line -> "|" + line + "|").forEach(System.out::println);