string vs stringBuffer comparison (#15306)

Co-authored-by: Sahil <sahilsriv05@gmail.com>

core-java-modules/core-java-strings/src/test/java/com/baeldung/stringIterator/StringIteratorTest.java

@@ -17,7 +17,7 @@ public class StringIteratorTest {
     public void whenUseJavaForLoop_thenIterate() {
         String input = "Hello, Baeldung!";
         String expectedOutput = "Hello, Baeldung!";
-        String result = StringIterator.javaForLoop(input);
+        String result = StringIterator.javaforLoop(input);
         assertEquals(expectedOutput, result);
     }
   
@@ -25,7 +25,7 @@ public class StringIteratorTest {
     public void whenUseForEachMethod_thenIterate() {
         String input = "Hello, Baeldung!";
         String expectedOutput = "Hello, Baeldung!";
-        String result = StringIterator.java8ForEach(input);
+        String result = StringIterator.java8forEach(input);
         assertEquals(expectedOutput, result);
     }
   

core-java-modules/core-java-strings/src/test/java/com/baeldung/stringbuffer/ComparePerformanceTest.java

@@ -0,0 +1,32 @@
+package com.baeldung.stringbuffer;
+
+import org.junit.Test;
+import static org.assertj.core.api.Assertions.assertThat;
+
+
+public class ComparePerformanceTest {
+
+    ComparePerformance cp = new ComparePerformance();
+
+    @Test
+    public void whenStringConcatenated_thenResultAsExpected() {
+        assertThat(cp.benchmarkStringConcatenation()).isEqualTo("springframework");
+    }
+
+    @Test
+    public void whenStringBufferConcatenated_thenResultAsExpected() {
+        StringBuffer stringBuffer = new StringBuffer("springframework");
+        assertThat(cp.benchmarkStringBufferConcatenation()).isEqualToIgnoringCase(stringBuffer);
+    }
+
+    @Test
+    public void whenStringReplaced_thenResultAsExpected() {
+        assertThat(cp.benchmarkStringReplacement()).isEqualTo("java-framework");
+    }
+
+    @Test
+    public void whenStringBufferReplaced_thenResultAsExpected() {
+        StringBuffer stringBuffer = new StringBuffer("java-framework");
+        assertThat(cp.benchmarkStringBufferReplacement()).isEqualToIgnoringCase(stringBuffer);
+    }
+}

core-java-modules/core-java-strings/src/test/java/com/baeldung/stringbuffer/HashCodeTest.java

@@ -0,0 +1,24 @@
+package com.baeldung.stringbuffer;
+
+import org.junit.Test;
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class HashCodeTest {
+
+    String str = "Spring";
+    StringBuffer sBuf = new StringBuffer("Spring");
+
+    @Test
+    public void whenStringConcat_thenHashCodeChanges() {
+        HashCode hc = new HashCode();
+
+        long initialStringHashCode = hc.getHashCodeString(str);
+        long initialSBufHashCode =  hc.getHashCodeSBuffer(sBuf);
+
+        str += "Framework";
+        sBuf.append("Framework");
+
+        assertThat(initialStringHashCode).isNotEqualTo(hc.getHashCodeString(str));
+        assertThat(initialSBufHashCode).isEqualTo(hc.getHashCodeSBuffer(sBuf));
+    }
+}