feature: Implement HasPlaceholder. Fixes #4068

flow-server/src/main/java/com/vaadin/flow/component/HasPlaceholder.java

@@ -0,0 +1,35 @@
+package com.vaadin.flow.component;
+
+/**
+ * A component which supports a placeholder.
+ * <p>
+ * A placeholder is a text that should be displayed in the input element,
+ * when the user has not entered a value.
+ * <p>
+ * The default implementations sets the <code>placeholder</code> property for this element.
+ * Override all methods in this interface if the placeholder
+ * should be set in some other way.
+ */
+public interface HasPlaceholder extends HasElement {
+    /**
+     * Sets the placeholder text that should be displayed in the input element,
+     * when the user has not entered a value
+     *
+     * @param placeholder the placeholder text, may be null.
+     */
+    default void setPlaceholder(String placeholder) {
+        getElement().setProperty("placeholder",
+                placeholder == null ? "" : placeholder);
+    }
+
+    /**
+     * The placeholder text that should be displayed in the input element, when
+     * the user has not entered a value
+     *
+     * @return the {@code placeholder} property from the web component. May be
+     * null if not yet set.
+     */
+    default String getPlaceholder() {
+        return getElement().getProperty("placeholder");
+    }
+}

flow-server/src/test/java/com/vaadin/flow/component/HasPlaceholderTest.java

@@ -0,0 +1,59 @@
+/*
+ * Copyright 2000-2023 Vaadin Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not
+ * use this file except in compliance with the License. You may obtain a copy of
+ * the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations under
+ * the License.
+ */
+package com.vaadin.flow.component;
+
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
+
+public class HasPlaceholderTest {
+
+    @Tag(Tag.DIV)
+    private static class TestComponent extends Component implements HasPlaceholder {
+
+    }
+
+    @Test
+    public void withoutPlaceholderComponent_getPlaceholderReturnsNull() {
+        TestComponent component = new TestComponent();
+
+        assertNull(component.getPlaceholder());
+    }
+
+    @Test
+    public void withNullPlaceholder_getPlaceholderReturnsEmptyString() {
+        TestComponent component = new TestComponent();
+        component.setPlaceholder(null);
+        assertEquals("", component.getPlaceholder());
+    }
+
+    @Test
+    public void withEmptyPlaceholder_getPlaceholderReturnsEmptyString() {
+        TestComponent component = new TestComponent();
+        component.setPlaceholder("");
+        assertEquals("", component.getPlaceholder());
+    }
+
+    @Test
+    public void setPlaceholder() {
+        TestComponent component = new TestComponent();
+        component.setPlaceholder("test Placeholder");
+
+        assertEquals("test Placeholder", component.getPlaceholder());
+    }
+
+}