diff --git a/spring-boot-project/spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/jar/StringSequenceTests.java b/spring-boot-project/spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/jar/StringSequenceTests.java
index d61f59f1d89..fddd5ee72a2 100644
--- a/spring-boot-project/spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/jar/StringSequenceTests.java
+++ b/spring-boot-project/spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/jar/StringSequenceTests.java
@@ -127,9 +127,9 @@ class StringSequenceTests {
 	@Test
 	void indexOfStringShouldReturnIndexOf() {
 		StringSequence sequence = new StringSequence("aabbaacc");
-		assertThat(sequence.indexOf("a")).isEqualTo(0);
-		assertThat(sequence.indexOf("b")).isEqualTo(2);
-		assertThat(sequence.subSequence(2).indexOf("a")).isEqualTo(2);
+		assertThat(sequence.indexOf('a')).isEqualTo(0);
+		assertThat(sequence.indexOf('b')).isEqualTo(2);
+		assertThat(sequence.subSequence(2).indexOf('a')).isEqualTo(2);
 	}
 
 	@Test
diff --git a/spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/it/run-profiles-fork/src/main/java/org/test/SampleApplication.java b/spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/it/run-profiles-fork/src/main/java/org/test/SampleApplication.java
index 67f8135ee35..e2dd8264196 100644
--- a/spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/it/run-profiles-fork/src/main/java/org/test/SampleApplication.java
+++ b/spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/it/run-profiles-fork/src/main/java/org/test/SampleApplication.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2017 the original author or authors.
+ * Copyright 2012-2019 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -28,7 +28,7 @@ public class SampleApplication {
 		if (!argument.startsWith("--spring.profiles.active=")) {
 			throw new IllegalArgumentException("Invalid argument " + argument);
 		}
-		int index = args[0].indexOf("=");
+		int index = args[0].indexOf('=');
 		String profile = argument.substring(index + 1);
 		System.out.println("I haz been run with profile(s) '" + profile + "'");
 	}
diff --git a/spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/it/run-profiles/src/main/java/org/test/SampleApplication.java b/spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/it/run-profiles/src/main/java/org/test/SampleApplication.java
index 67f8135ee35..e2dd8264196 100644
--- a/spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/it/run-profiles/src/main/java/org/test/SampleApplication.java
+++ b/spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/it/run-profiles/src/main/java/org/test/SampleApplication.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2017 the original author or authors.
+ * Copyright 2012-2019 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -28,7 +28,7 @@ public class SampleApplication {
 		if (!argument.startsWith("--spring.profiles.active=")) {
 			throw new IllegalArgumentException("Invalid argument " + argument);
 		}
-		int index = args[0].indexOf("=");
+		int index = args[0].indexOf('=');
 		String profile = argument.substring(index + 1);
 		System.out.println("I haz been run with profile(s) '" + profile + "'");
 	}
diff --git a/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/diagnostics/analyzer/BindFailureAnalyzerTests.java b/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/diagnostics/analyzer/BindFailureAnalyzerTests.java
index 5a450063940..2d7ad180d3e 100644
--- a/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/diagnostics/analyzer/BindFailureAnalyzerTests.java
+++ b/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/diagnostics/analyzer/BindFailureAnalyzerTests.java
@@ -108,7 +108,7 @@ class BindFailureAnalyzerTests {
 		MutablePropertySources sources = context.getEnvironment().getPropertySources();
 		Map<String, Object> map = new HashMap<>();
 		for (String pair : environment) {
-			int index = pair.indexOf("=");
+			int index = pair.indexOf('=');
 			String key = (index > 0) ? pair.substring(0, index) : pair;
 			String value = (index > 0) ? pair.substring(index + 1) : "";
 			map.put(key.trim(), value.trim());
diff --git a/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/diagnostics/analyzer/BindValidationFailureAnalyzerTests.java b/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/diagnostics/analyzer/BindValidationFailureAnalyzerTests.java
index c7740cb0665..d5a5714ea86 100644
--- a/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/diagnostics/analyzer/BindValidationFailureAnalyzerTests.java
+++ b/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/diagnostics/analyzer/BindValidationFailureAnalyzerTests.java
@@ -119,7 +119,7 @@ class BindValidationFailureAnalyzerTests {
 		MutablePropertySources sources = context.getEnvironment().getPropertySources();
 		Map<String, Object> map = new HashMap<>();
 		for (String pair : environment) {
-			int index = pair.indexOf("=");
+			int index = pair.indexOf('=');
 			String key = (index > 0) ? pair.substring(0, index) : pair;
 			String value = (index > 0) ? pair.substring(index + 1) : "";
 			map.put(key.trim(), value.trim());
diff --git a/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/diagnostics/analyzer/UnboundConfigurationPropertyFailureAnalyzerTests.java b/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/diagnostics/analyzer/UnboundConfigurationPropertyFailureAnalyzerTests.java
index 95edaed6dfa..0ea6eeb5620 100644
--- a/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/diagnostics/analyzer/UnboundConfigurationPropertyFailureAnalyzerTests.java
+++ b/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/diagnostics/analyzer/UnboundConfigurationPropertyFailureAnalyzerTests.java
@@ -91,7 +91,7 @@ class UnboundConfigurationPropertyFailureAnalyzerTests {
 		MutablePropertySources sources = context.getEnvironment().getPropertySources();
 		Map<String, Object> map = new HashMap<>();
 		for (String pair : environment) {
-			int index = pair.indexOf("=");
+			int index = pair.indexOf('=');
 			String key = (index > 0) ? pair.substring(0, index) : pair;
 			String value = (index > 0) ? pair.substring(index + 1) : "";
 			map.put(key.trim(), value.trim());
diff --git a/spring-boot-tests/spring-boot-smoke-tests/spring-boot-smoke-test-data-jpa/src/main/java/smoketest/data/jpa/service/CityServiceImpl.java b/spring-boot-tests/spring-boot-smoke-tests/spring-boot-smoke-test-data-jpa/src/main/java/smoketest/data/jpa/service/CityServiceImpl.java
index 7eaf4142959..1a9bc45de22 100644
--- a/spring-boot-tests/spring-boot-smoke-tests/spring-boot-smoke-test-data-jpa/src/main/java/smoketest/data/jpa/service/CityServiceImpl.java
+++ b/spring-boot-tests/spring-boot-smoke-tests/spring-boot-smoke-test-data-jpa/src/main/java/smoketest/data/jpa/service/CityServiceImpl.java
@@ -50,7 +50,7 @@ class CityServiceImpl implements CityService {
 		}
 
 		String country = "";
-		int splitPos = name.lastIndexOf(",");
+		int splitPos = name.lastIndexOf(',');
 
 		if (splitPos >= 0) {
 			country = name.substring(splitPos + 1);