Reduce the overhead of char[] creation

See gh-24204

Author: mdeinum

spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/health/SimpleHttpCodeStatusMapper.java

@@ -81,7 +81,8 @@ private static String getUniformCode(String code) {
 			return null;
 		}
 		StringBuilder builder = new StringBuilder();
-		for (char ch : code.toCharArray()) {
+		for (int i = 0; i < code.length(); i++) {
+			char ch = code.charAt(i);
 			if (Character.isAlphabetic(ch) || Character.isDigit(ch)) {
 				builder.append(Character.toLowerCase(ch));
 			}

spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/health/SimpleStatusAggregator.java

@@ -89,7 +89,8 @@ private static String getUniformCode(String code) {
 			return null;
 		}
 		StringBuilder builder = new StringBuilder();
-		for (char ch : code.toCharArray()) {
+		for (int i = 0; i < code.length(); i++) {
+			char ch = code.charAt(i);
 			if (Character.isAlphabetic(ch) || Character.isDigit(ch)) {
 				builder.append(Character.toLowerCase(ch));
 			}

spring-boot-project/spring-boot-tools/spring-boot-configuration-processor/src/main/java/org/springframework/boot/configurationprocessor/metadata/ConfigurationMetadata.java

@@ -189,7 +189,8 @@ public static String nestedPrefix(String prefix, String name) {
 	static String toDashedCase(String name) {
 		StringBuilder dashed = new StringBuilder();
 		Character previous = null;
-		for (char current : name.toCharArray()) {
+		for (int i = 0; i < name.length(); i++) {
+			char current = name.charAt(i);
 			if (SEPARATORS.contains(current)) {
 				dashed.append("-");
 			}

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/env/ConfigTreePropertySource.java

@@ -308,7 +308,8 @@ private String autoTrimTrailingNewLine(String string) {
 				return string;
 			}
 			int numberOfLines = 0;
-			for (char ch : string.toCharArray()) {
+			for (int i = 0; i < string.length(); i++) {
+				char ch = string.charAt(i);
 				if (ch == '\n') {
 					numberOfLines++;
 				}