rename akka-docs dir to docs (#62)

docs/src/test/java/jdocs/stream/SilenceSystemOut.java

@@ -0,0 +1,68 @@
+/*
+ * Copyright (C) 2018-2022 Lightbend Inc. <https://www.lightbend.com>
+ */
+
+package jdocs.stream;
+
+import org.apache.pekko.actor.ActorRef;
+
+import java.util.function.Predicate;
+
+/**
+ * Acts as if `System.out.println()` yet swallows all messages. Useful for putting printlines in
+ * examples yet without polluting the build with them.
+ */
+public class SilenceSystemOut {
+
+  private SilenceSystemOut() {}
+
+  public static System get() {
+    return new System(
+        new System.Println() {
+          @Override
+          public void println(String s) {
+            // ignore
+          }
+        });
+  }
+
+  public static System get(ActorRef probe) {
+    return new System(
+        new System.Println() {
+          @Override
+          public void println(String s) {
+            probe.tell(s, ActorRef.noSender());
+          }
+        });
+  }
+
+  public static System get(Predicate<String> filter, ActorRef probe) {
+    return new System(
+        new System.Println() {
+          @Override
+          public void println(String s) {
+            if (filter.test(s)) probe.tell(s, ActorRef.noSender());
+          }
+        });
+  }
+
+  public static class System {
+    public final Println out;
+
+    public System(Println out) {
+      this.out = out;
+    }
+
+    public abstract static class Println {
+      public abstract void println(String s);
+
+      public void println(Object s) {
+        println(s.toString());
+      }
+
+      public void printf(String format, Object... args) {
+        println(String.format(format, args));
+      }
+    }
+  }
+}