Add chapters 18-20 for the java book

Java-Kompendium/kap18/1/Schlafen.java

@@ -0,0 +1,24 @@
+import java.io.BufferedReader;
+import java.io.InputStreamReader;
+import java.io.IOException;
+
+public class Schlafen extends Thread {
+    @Override
+    public void run() {
+        var inputStream = new InputStreamReader(System.in);
+        var bufferedReader = new BufferedReader(inputStream);
+        int seconds;
+
+        System.out.println("Wieviele Sekunden soll ich warten?");
+        try {
+            var input = bufferedReader.readLine();
+            seconds = Integer.parseInt(input);
+        } catch (IOException exception) {
+            seconds = 0;
+        }
+        try {
+            Thread.sleep(seconds * 1000);
+        } catch (InterruptedException exception) {
+        }
+    }
+}