# HG changeset patch
# User redestad
# Date 1589883585 -7200
#      Tue May 19 12:19:45 2020 +0200
# Node ID 3031b5c094e37400ae4e9174462d5378a66fe6e7
# Parent  867c7b8ff48a25da642cf946bd48503c0259d1d7
8215401: Add isEmpty default method to CharSequence
Reviewed-by: jlaskey, rriggs, jjg

diff --git a/src/java.base/share/classes/java/lang/CharSequence.java b/src/java.base/share/classes/java/lang/CharSequence.java
--- a/src/java.base/share/classes/java/lang/CharSequence.java
+++ b/src/java.base/share/classes/java/lang/CharSequence.java
@@ -88,6 +88,21 @@
     char charAt(int index);
 
     /**
+     * Returns {@code true} if this character sequence is empty.
+     *
+     * @implNote
+     * The default implementation returns the result of calling {@code length() == 0}.
+     *
+     * @return {@code true} if {@link #length()} is {@code 0}, otherwise
+     * {@code false}
+     *
+     * @since 15
+     */
+    default boolean isEmpty() {
+        return this.length() == 0;
+    }
+
+    /**
      * Returns a {@code CharSequence} that is a subsequence of this sequence.
      * The subsequence starts with the {@code char} value at the specified index and
      * ends with the {@code char} value at index {@code end - 1}.  The length
diff --git a/src/java.base/share/classes/java/lang/String.java b/src/java.base/share/classes/java/lang/String.java
--- a/src/java.base/share/classes/java/lang/String.java
+++ b/src/java.base/share/classes/java/lang/String.java
@@ -684,6 +684,7 @@
      *
      * @since 1.6
      */
+    @Override
     public boolean isEmpty() {
         return value.length == 0;
     }
diff --git a/test/jdk/java/lang/CharSequence/Emptiness.java b/test/jdk/java/lang/CharSequence/Emptiness.java
new file mode 100644
--- /dev/null
+++ b/test/jdk/java/lang/CharSequence/Emptiness.java
@@ -0,0 +1,81 @@
+/*
+ * Copyright (c) 2020, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+import java.nio.CharBuffer;
+import java.util.Iterator;
+import java.util.Set;
+import java.util.TreeSet;
+import org.testng.Assert;
+import org.testng.annotations.Test;
+
+/**
+ * @test
+ * @bug 8215401
+ * @summary Test to verify the isEmpty method is behaviorally consistent
+ *          with length
+ * @run testng Emptiness
+ */
+public class Emptiness {
+
+    @Test
+    public void isEmpty() {
+        checkEmpty(new StringBuilder());
+        checkEmpty(new StringBuffer());
+        checkEmpty("");
+        checkEmpty(new CharSequence() {
+            @Override public int length() { return 0; }
+            @Override public char charAt(int index) { return 'f'; }
+            @Override public CharSequence subSequence(int start, int end) {
+                throw new UnsupportedOperationException();
+            }
+        });
+    }
+
+    @Test
+    public void isNotEmpty() {
+        checkNotEmpty(new StringBuilder().append("foo"));
+        checkNotEmpty(new StringBuffer().append("bar"));
+        checkNotEmpty("baz");
+        checkNotEmpty(new CharSequence() {
+            @Override public int length() { return 1; }
+            @Override public char charAt(int index) { return 'f'; }
+            @Override public CharSequence subSequence(int start, int end) {
+                throw new UnsupportedOperationException();
+            }
+        });
+    }
+
+    public void checkEmpty(CharSequence cs) {
+        Assert.assertTrue(cs.isEmpty());
+        Assert.assertTrue(consistentWithLength(cs));
+    }
+
+    public void checkNotEmpty(CharSequence cs) {
+        Assert.assertTrue(!cs.isEmpty());
+        Assert.assertTrue(consistentWithLength(cs));
+    }
+
+    public boolean consistentWithLength(CharSequence cs) {
+        return cs.isEmpty() == (cs.length() == 0);
+    }
+}