8342936: Enhance java.io.IO with parameter-less println() and readln()

Reviewed-by: asotona, jpai, naoto

src/java.base/share/classes/java/io/Console.java

@@ -172,6 +172,19 @@ public sealed class Console implements Flushable permits ProxyingConsole {
         throw newUnsupportedOperationException();
     }
 
+    /**
+     * Terminates the current line in this console's output stream using
+     * {@link System#lineSeparator()} and then flushes the console.
+     *
+     * @return  This console
+     *
+     * @since 24
+     */
+    @PreviewFeature(feature = PreviewFeature.Feature.IMPLICIT_CLASSES)
+    public Console println() {
+        return println("");
+    }
+
     /**
      * Writes a string representation of the specified object to this console's
      * output stream and then flushes the console.
@@ -214,6 +227,24 @@ public sealed class Console implements Flushable permits ProxyingConsole {
         throw newUnsupportedOperationException();
     }
 
+    /**
+     * Reads a single line of text from this console.
+     *
+     * @throws IOError
+     *         If an I/O error occurs.
+     *
+     * @return  A string containing the line read from the console, not
+     *          including any line-termination characters, or {@code null}
+     *          if an end of stream has been reached without having read
+     *          any characters.
+     *
+     * @since 24
+     */
+    @PreviewFeature(feature = PreviewFeature.Feature.IMPLICIT_CLASSES)
+    public String readln() {
+        throw newUnsupportedOperationException();
+    }
+
     /**
      * Writes a formatted string to this console's output stream using
      * the specified format string and arguments with the

src/java.base/share/classes/java/io/IO.java

@@ -63,6 +63,21 @@ public final class IO {
         con().println(obj);
     }
 
+    /**
+     * Terminates the current line on the system console and then flushes
+     * that console.
+     *
+     * <p> The effect is as if {@link Console#println() println()}
+     * had been called on {@code System.console()}.
+     *
+     * @throws IOError if {@code System.console()} returns {@code null},
+     *                 or if an I/O error occurs
+     * @since 24
+     */
+    public static void println() {
+        con().println();
+    }
+
     /**
      * Writes a string representation of the specified object to the system
      * console and then flushes that console.
@@ -99,6 +114,24 @@ public final class IO {
         return con().readln(prompt);
     }
 
+    /**
+     * Reads a single line of text from the system console.
+     *
+     * <p> The effect is as if {@link Console#readln() readln()}
+     * had been called on {@code System.console()}.
+     *
+     * @return a string containing the line read from the system console, not
+     * including any line-termination characters. Returns {@code null} if an
+     * end of stream has been reached without having read any characters.
+     *
+     * @throws IOError if {@code System.console()} returns {@code null},
+     *                 or if an I/O error occurs
+     * @since 24
+     */
+    public static String readln() {
+        return con().readln();
+    }
+
     private static Console con() {
         var con = System.console();
         if (con != null) {

src/java.base/share/classes/java/io/ProxyingConsole.java

@@ -117,6 +117,18 @@ final class ProxyingConsole extends Console {
         }
     }
 
+    /**
+     * {@inheritDoc}
+     *
+     * @throws IOError {@inheritDoc}
+     */
+    @Override
+    public String readln() {
+        synchronized (readLock) {
+            return delegate.readln();
+        }
+    }
+
     /**
      * {@inheritDoc}
      */