Use StringBuilder/StringJoiner for concatenation String's in loop

ajde/src/main/java/org/aspectj/ajde/internal/LstBuildConfigFileUpdater.java

 
 	public void writeConfigFile(String filePath, List<BuildConfigNode> files, List<BuildConfigNode> importedNodes) {
 		// Set contentsSet = new TreeSet(fileContents);
-		String fileContentsString = "";
+		StringBuilder fileContentsString = new StringBuilder();
 		// List filesToWrite = null;
 		Set<String> includedFiles = new HashSet<>();
 		for (BuildConfigNode node : importedNodes) {
-			fileContentsString += '@' + node.getResourcePath() + "\n";
+			fileContentsString.append('@').append(node.getResourcePath()).append("\n");
 			String parentPath = new File(filePath).getParent();
 			String importedFilePath = parentPath + File.separator + node.getResourcePath();
 			includedFiles.addAll(getIncludedFiles(importedFilePath, parentPath));
 
 		for (BuildConfigNode node : files) {
 			if (node.getName().endsWith(".lst") && !node.getResourcePath().startsWith("..")) {
-				fileContentsString += '@';
-				fileContentsString += node.getResourcePath() + "\n";
+				fileContentsString.append('@');
+				fileContentsString.append(node.getResourcePath()).append("\n");
 			} else {
 				if (!includedFiles.contains(node.getResourcePath())) {
-					fileContentsString += node.getResourcePath() + "\n";
+					fileContentsString.append(node.getResourcePath()).append("\n");
 				}
 			}
 		}
-		writeFile(fileContentsString, filePath);
+		writeFile(fileContentsString.toString(), filePath);
 	}
 
 	private List<String> getIncludedFiles(String path, String rootPath) {

ajde/src/main/java/org/aspectj/ajde/ui/internal/UserPreferencesStore.java

 
 	@Override
 	public void setProjectMultivalPreference(String name, List values) {
-		String valuesString = "";
+		StringBuilder valuesString = new StringBuilder();
 		for (Object value : values) {
-			valuesString += (String) value + ';';
+			valuesString.append((String)value).append(';');
 		}
-		properties.setProperty(name, valuesString);
+		properties.setProperty(name, valuesString.toString());
 		saveProperties();
 	}
 

ajdoc/src/main/java/org/aspectj/tools/ajdoc/HtmlDecorator.java

 	static void decorateDocWithRel(IProgramElement node, StringBuilder fileContentsBuffer, int index, List targets,
 			HtmlRelationshipKind relKind) {
 		if (targets != null && !targets.isEmpty()) {
-			String adviceDoc = "<TABLE WIDTH=\"100%\" BGCOLOR=#FFFFFF><TR>"
-					+ "<TD width=\"15%\" bgcolor=\"#FFD8B0\"><B><FONT COLOR=000000>" + relKind.toString() + "</font></b></td><td>";
+			StringBuilder adviceDoc = new StringBuilder("<TABLE WIDTH=\"100%\" BGCOLOR=#FFFFFF><TR>"
+					+ "<TD width=\"15%\" bgcolor=\"#FFD8B0\"><B><FONT COLOR=000000>" + relKind.toString() + "</font></b></td><td>");
 
 			String relativePackagePath = getRelativePathFromHere(node.getPackageName().replace('.', '/') + Config.DIR_SEP_CHAR);
 
 				hrefLink += sbuff.toString() + ".html" + "#" + sb.toString();
 
 				if (!addedNames.contains(hrefName)) {
-					adviceDoc = adviceDoc + "<A HREF=\"" + hrefLink + "\"><tt>" + hrefName.replace('/', '.') + "</tt></A>";
+					adviceDoc.append("<A HREF=\"").append(hrefLink).append("\"><tt>").append(hrefName.replace('/', '.')).append("</tt></A>");
 
 					if (it.hasNext())
-						adviceDoc += ", ";
+						adviceDoc.append(", ");
 					addedNames.add(hrefName);
 				}
 			}
-			adviceDoc += "</TR></TD></TABLE>\n";
-			fileContentsBuffer.insert(index, adviceDoc);
+			adviceDoc.append("</TR></TD></TABLE>\n");
+			fileContentsBuffer.insert(index, adviceDoc.toString());
 		}
 	}
 
 		}
 		if (targets == null)
 			return "";
-		String entry = "<TABLE WIDTH=\"100%\" BGCOLOR=#FFFFFF><TR>";
+		StringBuilder entry = new StringBuilder("<TABLE WIDTH=\"100%\" BGCOLOR=#FFFFFF><TR>");
 
 		IProgramElement.Kind kind = decl.getKind();
 		if (kind.equals(IProgramElement.Kind.ADVICE)) {
-			entry += "<TD width=\"10%\" bgcolor=\"#FFD8B0\"><B><FONT COLOR=000000>" + HtmlRelationshipKind.ADVISES.toString()
-					+ "</b></font></td><td>";
+			entry.append("<TD width=\"10%\" bgcolor=\"#FFD8B0\"><B><FONT COLOR=000000>")
+					.append(HtmlRelationshipKind.ADVISES)
+					.append("</b></font></td><td>");
 		} else if (kind.equals(IProgramElement.Kind.DECLARE_WARNING) || kind.equals(IProgramElement.Kind.DECLARE_ERROR)) {
-			entry += "<TD width=\"10%\" bgcolor=\"#FFD8B0\"><B><FONT COLOR=000000>" + HtmlRelationshipKind.MATCHED_BY.toString()
-					+ "</b></font></td><td>";
+			entry.append("<TD width=\"10%\" bgcolor=\"#FFD8B0\"><B><FONT COLOR=000000>")
+					.append(HtmlRelationshipKind.MATCHED_BY)
+					.append("</b></font></td><td>");
 		} else if (kind.isDeclareAnnotation()) {
-			entry += "<TD width=\"10%\" bgcolor=\"#FFD8B0\"><B><FONT COLOR=000000>" + HtmlRelationshipKind.ANNOTATES.toString()
-					+ "</b></font></td><td>";
+			entry.append("<TD width=\"10%\" bgcolor=\"#FFD8B0\"><B><FONT COLOR=000000>")
+					.append(HtmlRelationshipKind.ANNOTATES)
+					.append("</b></font></td><td>");
 		} else if (kind.equals(IProgramElement.Kind.DECLARE_SOFT)) {
-			entry += "<TD width=\"10%\" bgcolor=\"#FFD8B0\"><B><FONT COLOR=000000>" + HtmlRelationshipKind.SOFTENS.toString()
-					+ "</b></font></td><td>";
+			entry.append("<TD width=\"10%\" bgcolor=\"#FFD8B0\"><B><FONT COLOR=000000>")
+					.append(HtmlRelationshipKind.SOFTENS)
+					.append("</b></font></td><td>");
 		} else {
-			entry += "<TD width=\"10%\" bgcolor=\"#FFD8B0\"><B><FONT COLOR=000000>" + HtmlRelationshipKind.DECLARED_ON.toString()
-					+ "</b></font></td><td>";
+			entry.append("<TD width=\"10%\" bgcolor=\"#FFD8B0\"><B><FONT COLOR=000000>")
+					.append(HtmlRelationshipKind.DECLARED_ON)
+					.append("</b></font></td><td>");
 		}
 
 		String relativePackagePath = getRelativePathFromHere(decl.getPackageName().replace('.', '/') + Config.DIR_SEP_CHAR);
 				}
 
 				if (!addedNames.contains(hrefName)) {
-					entry += "<A HREF=\"" + hrefLink + "\"><tt>" + hrefName.replace('/', '.') + "</tt></A>"; // !!! don't replace
+					entry.append("<A HREF=\"").append(hrefLink).append("\"><tt>").append(hrefName.replace('/', '.')).append("</tt></A>"); // !!! don't replace
 					if (it.hasNext())
-						entry += ", ";
+						entry.append(", ");
 					addedNames.add(hrefName);
 				}
 			}
 		}
-		entry += "</B></FONT></TD></TR></TABLE>\n</TR></TD>\n";
-		return entry;
+		entry.append("</B></FONT></TD></TR></TABLE>\n</TR></TD>\n");
+		return entry.toString();
 	}
 
 	/**
 		if (comment == null)
 			return "";
 
-		String formattedComment = "";
+		StringBuilder formattedComment = new StringBuilder();
 		// strip the comment markers
 
 		int startIndex = comment.indexOf("/**");
 				// if ( linkIndex != -1 ) {
 				// line = line.substring(0, linkIndex) + line.substring(linkIndex);
 				// }
-				formattedComment += line;
+				formattedComment.append(line);
 			}
 		} catch (IOException ioe) {
 			throw new Error("Couldn't format comment for declaration: " + decl.getName());
 		}
-		return formattedComment;
+		return formattedComment.toString();
 	}
 
 	static public IProgramElement[] getProgramElements(AsmManager model, String filename) {

org.aspectj.ajdt.core/src/main/java/org/aspectj/ajdt/internal/core/builder/AsmElementFormatter.java

 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
+import java.util.StringJoiner;
 
 import org.aspectj.ajdt.internal.compiler.ast.AdviceDeclaration;
 import org.aspectj.ajdt.internal.compiler.ast.DeclareDeclaration;
 	}
 
 	private String genPrecedenceListLabel(TypePatternList list) {
-		String tpList = "";
+		StringJoiner tpList = new StringJoiner(", ");
 		for (int i = 0; i < list.size(); i++) {
-			tpList += genTypePatternLabel(list.get(i));
-			if (i < list.size() - 1) {
-				tpList += ", ";
-			}
+			tpList.add(genTypePatternLabel(list.get(i)));
 		}
-		return tpList;
+		return tpList.toString();
 	}
 
 	// private String genArguments(MethodDeclaration md) {

taskdefs/src/main/java/org/aspectj/tools/ant/taskdefs/Ajdoc.java

 import java.util.Collections;
 import java.util.Enumeration;
 import java.util.HashMap;
-import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
+import java.util.StringJoiner;
 import java.util.StringTokenizer;
 import java.util.Vector;
 
         }
         for (String title: groupMap.keySet()) {
             List<String> packages = groupMap.get(title);
-            String pkgstr = "";
-            for (Iterator<String> j = packages.iterator(); j.hasNext();) {
-                pkgstr += j.next();
-                if (j.hasNext()) pkgstr += ",";
+            StringJoiner pkgstr = new StringJoiner(",");
+            for (String aPackage : packages) {
+                pkgstr.add(aPackage);
             }
             cmd.createArgument().setValue("-group");
             cmd.createArgument().setValue(title);
-            cmd.createArgument().setValue(pkgstr);
+            cmd.createArgument().setValue(pkgstr.toString());
         }
         if (argfiles != null) {
 			for (File file : argfiles) {