JavaUtils/Java11.java

import java.awt.Point;
import java.io.IOException;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.*;
import java.util.function.Predicate;
import java.util.stream.Collectors;

class Java11 {
   public static void main(String[] args) {
      ////////
      // 1. //
      ////////
      // if the resource is referenced by a final or effectively final variable,
      // a try-with-resources statement can manage a resource without a new variable being declared:
      MyAutoCloseable mac = new MyAutoCloseable();
      try (mac) {
         // do some stuff with mac
      }

      ////////
      // 2. //
      ////////
      // use diamond operator in conjunction with anonymous inner classes
      List<Integer> fc = new ArrayList<>(1) {}; // anonymous inner class

      List<? extends Integer> fc0 = new ArrayList<>(1) {
         // anonymous inner class
      };

      List<?> fc1 = new ArrayList<>(1) {}; // anonymous inner class

      ////////
      // 4. //
      ////////
      // Local Variable Type Inference
      var message = "Hello, Java 10";
      var point = new Point(1, 2);

      ////////
      // 5. //
      ////////
      // immutable Collections/ Maps
      Map<String, Integer> meineMap = Map.of();
      Set<String> meinSet = Set.of("key1", "key2", "key3");
      List<String> meineListe = List.copyOf(meinSet);

      ////////
      // 6. //
      ////////
      // Optional to Stream Optional.stream() gives us an easy way to you use the power of Streams on Optional elements
      List<String> filteredList = new ArrayList<Optional<String>>().stream()
         .flatMap(Optional::stream)
         .collect(Collectors.toList());

      ////////
      // 7. //
      ////////
      // Collectors get additional methods to collect a Stream into unmodifiable List, Map or Set:
      List<Integer> evenList = new ArrayList<Integer>().stream()
         .filter(i -> i % 2 == 0)
         .collect(Collectors.toUnmodifiableList());

      ////////
      // 8. //
      ////////
      // Optional got a new method orElseThrow() which doesn’t take any argument and throws NoSuchElementException if no value is present:
      Integer firstEven = List.of(1, 2, 3).stream()
         .filter(i -> i % 2 == 0)
         .findFirst()
         .orElseThrow();

      ////////
      // 9. //
      ////////
      // Java 11 adds a few new methods to the String class
      var multilineString = "Baeldung helps \n \n developers \n explore Java.";
      List<String> lines = multilineString.lines().collect(Collectors.toList());
      assert "    ".isBlank();
      assert "    x    ".strip().equals("x");
      assert "    x    ".stripLeading().equals("x    ");
      assert "    x    ".stripTrailing().equals("    x");
      assert "x".repeat(5).equals("xxxxx");

      /////////
      // 10. //
      /////////
      // We can use the new readString and writeString static methods from the Files class:
      String fileContent = null;
      try {
         Path filePath = Files.writeString(Files.createTempFile("demo", ".txt"), "Sample text");
         fileContent = Files.readString(filePath);
      } catch (IOException ioe) {}
      assert fileContent.equals("Sample text");

      /////////
      // 11. //
      /////////
      // The java.util.Collection interface contains a new default toArray method which takes an IntFunction argument.
      List<String> sampleList = List.of("Java", "Kotlin");
      String[] sampleArray = sampleList.toArray(String[]::new);

      /////////
      // 12. //
      /////////
      // A static not method has been added to the Predicate interface.
      sampleList = List.of("Java", "\n \n", "Kotlin", " ");
      List<String> withoutBlanks = sampleList.stream()
         .filter(Predicate.not(String::isBlank))
         .collect(Collectors.toList());
      // While not(isBlank) reads more naturally than isBlank.negate(), the big advantage is that we can also use not with method references,
      // like not(String::isBlank).

      /////////
      // 13. //
      /////////
      // Support for using the local variable syntax (var keyword) in lambda parameters was added in Java 11.
      // We can make use of this feature to apply modifiers to our local variables, like defining a type annotation:
      sampleList = List.of("Java", "Kotlin");
      String resultString = sampleList.stream()
         .map((@Nonnull var x) -> x.toUpperCase())
         .collect(Collectors.joining(", "));
      assert resultString.equals("JAVA, KOTLIN");
   }
}

class MyAutoCloseable implements AutoCloseable {
   public void close() {}
}

////////
// 3. //
////////
// Interfaces in the upcoming JVM version can have private methods, which can be used to split lengthy default methods
interface InterfaceWithPrivateMethods {
   private static String staticPrivate() {
      return "static private";
   }

   private String instancePrivate() {
      return "instance private";
   }

   default void check() {
      String result = staticPrivate();
      InterfaceWithPrivateMethods pvt = new InterfaceWithPrivateMethods() {
         // anonymous class
      };
      result = pvt.instancePrivate();
   }
}


@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.PARAMETER)
public @interface Nonnull {}