[11u]: RFR: 8215281: Use String.isEmpty() when applicable in java.base

[Langer, Christoph]

Hi,

please review the backport of the String.isEmpty() cleanups in java.base.

The main reason to bring this down to JDK11u is that it'll ease backporting of later changes which otherwise run into conflicts and won't resolve. Furthermore, the original change is a nice cleanup and improves performance.

Webrev: http://cr.openjdk.java.net/~clanger/webrevs/8215281.11u/
Bug: https://bugs.openjdk.java.net/browse/JDK-8215281
Change in jdk/jdk: http://hg.openjdk.java.net/jdk/jdk/rev/8bf9268df0e2

The original patch merely applies (with a little fuzz in some places). There were 4 rejects:

src/java.base/share/classes/java/lang/VersionProps.java.template
--- VersionProps.java.template
+++ VersionProps.java.template
@@ -95,7 +95,7 @@
         props.put("java.version.date", java_version_date);
         props.put("java.runtime.version", java_runtime_version);
         props.put("java.runtime.name", java_runtime_name);
-        if (VENDOR_VERSION_STRING.length() > 0)
+        if (!VENDOR_VERSION_STRING.isEmpty())
             props.put("java.vendor.version", VENDOR_VERSION_STRING);
         props.put("java.class.version", CLASSFILE_MAJOR_MINOR);

-> manually resolved that to the right location

src/java.base/share/classes/java/text/CompactNumberFormat.java

-> file does not exist in 11u, so dropping

src/java.base/share/classes/jdk/internal/org/objectweb/asm/util/CheckMethodAdapter.java
--- CheckMethodAdapter.java
+++ CheckMethodAdapter.java
@@ -1314,7 +1314,7 @@
       * @param message the message to use in case of error.
       */
     static void checkMethodIdentifier(final int version, final String name, final String message) {
-        if (name == null || name.length() == 0) {
+        if (name == null || name.isEmpty()) {
             throw new IllegalArgumentException(INVALID + message + MUST_NOT_BE_NULL_OR_EMPTY);
         }
         if ((version & 0xFFFF) >= Opcodes.V1_5) {
@@ -1347,7 +1347,7 @@
       * @param message the message to use in case of error.
       */
     static void checkInternalName(final int version, final String name, final String message) {
-        if (name == null || name.length() == 0) {
+        if (name == null || name.isEmpty()) {
             throw new IllegalArgumentException(INVALID + message + MUST_NOT_BE_NULL_OR_EMPTY);
         }
         if (name.charAt(0) == '[') {
@@ -1457,7 +1457,7 @@
       * @param descriptor the string to be checked.
       */
     static void checkMethodDescriptor(final int version, final String descriptor) {
-        if (descriptor == null || descriptor.length() == 0) {
+        if (descriptor == null || descriptor.isEmpty()) {
             throw new IllegalArgumentException("Invalid method descriptor (must not be null or empty)");
         }
         if (descriptor.charAt(0) != '(' || descriptor.length() < 3) {

-> file looks different in 11u due to a missing change. So, modified the right places in the 11u version

src/java.base/share/classes/jdk/internal/org/objectweb/asm/util/CheckSignatureAdapter.java
--- CheckSignatureAdapter.java
+++ CheckSignatureAdapter.java
@@ -365,7 +365,7 @@
     }
     private void checkClassName(final String name, final String message) {
-        if (name == null || name.length() == 0) {
+        if (name == null || name.isEmpty()) {
             throw new IllegalArgumentException(INVALID + message + " (must not be null or empty)");
         }
         for (int i = 0; i < name.length(); ++i) {
@@ -377,7 +377,7 @@
     }
     private void checkIdentifier(final String name, final String message) {
-        if (name == null || name.length() == 0) {
+        if (name == null || name.isEmpty()) {
             throw new IllegalArgumentException(INVALID + message + " (must not be null or empty)");
         }
         for (int i = 0; i < name.length(); ++i) {

-> file looks different in 11u due to a missing change. So, modified the right places in the 11u version

Thanks
Christoph