From 5ff7c57f9ff5428ef3d2aedd7e860bb1e8ff29ea Mon Sep 17 00:00:00 2001
From: Shaojin Wen <shaojin.wensj@alibaba-inc.com>
Date: Fri, 26 Jul 2024 12:10:21 +0000
Subject: [PATCH] 8337168: Optimize LocalDateTime.toString

Reviewed-by: liach, naoto
---
 .../share/classes/java/time/LocalDate.java    | 20 +++++++++++++------
 .../classes/java/time/LocalDateTime.java      |  8 ++++++--
 .../share/classes/java/time/LocalTime.java    | 12 +++++++++--
 3 files changed, 30 insertions(+), 10 deletions(-)

diff --git a/src/java.base/share/classes/java/time/LocalDate.java b/src/java.base/share/classes/java/time/LocalDate.java
index b0d7ad33c8a..2d71fb1ceca 100644
--- a/src/java.base/share/classes/java/time/LocalDate.java
+++ b/src/java.base/share/classes/java/time/LocalDate.java
@@ -2147,11 +2147,20 @@ public final class LocalDate
      */
     @Override
     public String toString() {
+        var buf = new StringBuilder(10);
+        formatTo(buf);
+        return buf.toString();
+    }
+
+    /**
+     * Prints the toString result to the given buf, avoiding extra string allocations.
+     * Requires extra capacity of 10 to avoid StringBuilder reallocation.
+     */
+    void formatTo(StringBuilder buf) {
         int yearValue = year;
         int monthValue = month;
         int dayValue = day;
         int absYear = Math.abs(yearValue);
-        StringBuilder buf = new StringBuilder(10);
         if (absYear < 1000) {
             if (yearValue < 0) {
                 buf.append('-');
@@ -2164,11 +2173,10 @@ public final class LocalDate
             }
             buf.append(yearValue);
         }
-        return buf.append(monthValue < 10 ? "-0" : "-")
-            .append(monthValue)
-            .append(dayValue < 10 ? "-0" : "-")
-            .append(dayValue)
-            .toString();
+        buf.append(monthValue < 10 ? "-0" : "-")
+           .append(monthValue)
+           .append(dayValue < 10 ? "-0" : "-")
+           .append(dayValue);
     }
 
     //-----------------------------------------------------------------------
diff --git a/src/java.base/share/classes/java/time/LocalDateTime.java b/src/java.base/share/classes/java/time/LocalDateTime.java
index 024aa1dacbe..d14afb7d78f 100644
--- a/src/java.base/share/classes/java/time/LocalDateTime.java
+++ b/src/java.base/share/classes/java/time/LocalDateTime.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2012, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2012, 2024, 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
@@ -1965,7 +1965,11 @@ public final class LocalDateTime
      */
     @Override
     public String toString() {
-        return date.toString() + 'T' + time.toString();
+        var buf = new StringBuilder(29);
+        date.formatTo(buf);
+        buf.append('T');
+        time.formatTo(buf);
+        return buf.toString();
     }
 
     //-----------------------------------------------------------------------
diff --git a/src/java.base/share/classes/java/time/LocalTime.java b/src/java.base/share/classes/java/time/LocalTime.java
index fd2c5ce4d45..f28f8d3c599 100644
--- a/src/java.base/share/classes/java/time/LocalTime.java
+++ b/src/java.base/share/classes/java/time/LocalTime.java
@@ -1631,7 +1631,16 @@ public final class LocalTime
      */
     @Override
     public String toString() {
-        StringBuilder buf = new StringBuilder(18);
+        var buf = new StringBuilder(18);
+        formatTo(buf);
+        return buf.toString();
+    }
+
+    /**
+     * Prints the toString result to the given buf, avoiding extra string allocations.
+     * Requires extra capacity of 18 to avoid StringBuilder reallocation.
+     */
+    void formatTo(StringBuilder buf) {
         int hourValue = hour;
         int minuteValue = minute;
         int secondValue = second;
@@ -1657,7 +1666,6 @@ public final class LocalTime
                 buf.append(digits);
             }
         }
-        return buf.toString();
     }
 
     //-----------------------------------------------------------------------