diff --git a/runtime/Java/src/org/antlr/v4/runtime/atn/ATNConfigSet.java b/runtime/Java/src/org/antlr/v4/runtime/atn/ATNConfigSet.java
index 994bd6eb3..d64de3b5c 100755
--- a/runtime/Java/src/org/antlr/v4/runtime/atn/ATNConfigSet.java
+++ b/runtime/Java/src/org/antlr/v4/runtime/atn/ATNConfigSet.java
@@ -70,9 +70,9 @@ public class ATNConfigSet extends OrderedHashSet<ATNConfig> {
 	public String toString() {
 		StringBuilder buf = new StringBuilder();
 		buf.append(super.toString());
-		if ( hasSemanticContext ) buf.append(",hasSemanticContext="+hasSemanticContext);
-		if ( uniqueAlt!=ATN.INVALID_ALT_NUMBER ) buf.append(",uniqueAlt="+uniqueAlt);
-		if ( conflictingAlts!=null ) buf.append(",conflictingAlts="+conflictingAlts);
+		if ( hasSemanticContext ) buf.append(",hasSemanticContext=").append(hasSemanticContext);
+		if ( uniqueAlt!=ATN.INVALID_ALT_NUMBER ) buf.append(",uniqueAlt=").append(uniqueAlt);
+		if ( conflictingAlts!=null ) buf.append(",conflictingAlts=").append(conflictingAlts);
 		if ( dipsIntoOuterContext ) buf.append(",dipsIntoOuterContext");
 		return buf.toString();
 	}
diff --git a/runtime/Java/src/org/antlr/v4/runtime/dfa/DFASerializer.java b/runtime/Java/src/org/antlr/v4/runtime/dfa/DFASerializer.java
index face14f53..0b06d4c5a 100644
--- a/runtime/Java/src/org/antlr/v4/runtime/dfa/DFASerializer.java
+++ b/runtime/Java/src/org/antlr/v4/runtime/dfa/DFASerializer.java
@@ -60,7 +60,7 @@ public class DFASerializer {
 					if ( t!=null && t.stateNumber != Integer.MAX_VALUE ) {
 						buf.append(getStateString(s));
 						String label = getEdgeLabel(i);
-						buf.append("-"+label+"->"+ getStateString(t)+'\n');
+						buf.append("-").append(label).append("->").append(getStateString(t)).append('\n');
 					}
 				}
 			}
diff --git a/runtime/Java/src/org/antlr/v4/runtime/dfa/DFAState.java b/runtime/Java/src/org/antlr/v4/runtime/dfa/DFAState.java
index faf8806a8..98586b585 100644
--- a/runtime/Java/src/org/antlr/v4/runtime/dfa/DFAState.java
+++ b/runtime/Java/src/org/antlr/v4/runtime/dfa/DFAState.java
@@ -205,7 +205,7 @@ public class DFAState {
 	@Override
 	public String toString() {
         StringBuilder buf = new StringBuilder();
-        buf.append(stateNumber + ":" + configset);
+        buf.append(stateNumber).append(":").append(configset);
         if ( isAcceptState ) {
             buf.append("=>");
             if ( predicates!=null ) {
diff --git a/runtime/Java/src/org/antlr/v4/runtime/tree/gui/PostScriptDocument.java b/runtime/Java/src/org/antlr/v4/runtime/tree/gui/PostScriptDocument.java
index 06a092fc9..0672f6396 100644
--- a/runtime/Java/src/org/antlr/v4/runtime/tree/gui/PostScriptDocument.java
+++ b/runtime/Java/src/org/antlr/v4/runtime/tree/gui/PostScriptDocument.java
@@ -74,7 +74,7 @@ public class PostScriptDocument {
 	protected StringBuilder header() {
 		StringBuilder b = new StringBuilder();
 		b.append("%!PS-Adobe-3.0 EPSF-3.0\n");
-		b.append(boundingBox+"\n");
+		b.append(boundingBox).append("\n");
 		b.append("0.3 setlinewidth\n");
 		b.append("%% x y w h highlight\n" +
 				 "/highlight {\n" +
@@ -116,7 +116,7 @@ public class PostScriptDocument {
 
 	public void lineWidth(double w) {
 		lineWidth = w;
-		ps.append(w+" setlinewidth\n");
+		ps.append(w).append(" setlinewidth\n");
 	}
 
 	public void move(double x, double y) {
diff --git a/tool/src/org/antlr/v4/automata/ATNPrinter.java b/tool/src/org/antlr/v4/automata/ATNPrinter.java
index 41ced4639..db83c1fc5 100644
--- a/tool/src/org/antlr/v4/automata/ATNPrinter.java
+++ b/tool/src/org/antlr/v4/automata/ATNPrinter.java
@@ -73,33 +73,33 @@ public class ATNPrinter {
 				}
 				buf.append(getStateString(s));
 				if ( t instanceof EpsilonTransition ) {
-					buf.append("->"+ getStateString(t.target)+'\n');
+					buf.append("->").append(getStateString(t.target)).append('\n');
 				}
 				else if ( t instanceof RuleTransition ) {
-					buf.append("-"+g.getRule(((RuleTransition)t).ruleIndex).name+"->"+ getStateString(t.target)+'\n');
+					buf.append("-").append(g.getRule(((RuleTransition)t).ruleIndex).name).append("->").append(getStateString(t.target)).append('\n');
 				}
 				else if ( t instanceof ActionTransition ) {
 					ActionTransition a = (ActionTransition)t;
-					buf.append("-"+a.toString()+"->"+ getStateString(t.target)+'\n');
+					buf.append("-").append(a.toString()).append("->").append(getStateString(t.target)).append('\n');
 				}
 				else if ( t instanceof SetTransition ) {
 					SetTransition st = (SetTransition)t;
 					boolean not = st instanceof NotSetTransition;
 					if ( g.isLexer() ) {
-						buf.append("-"+(not?"~":"")+st.toString()+"->"+ getStateString(t.target)+'\n');
+						buf.append("-").append(not?"~":"").append(st.toString()).append("->").append(getStateString(t.target)).append('\n');
 					}
 					else {
-						buf.append("-"+(not?"~":"")+st.label().toString(g.getTokenNames())+"->"+ getStateString(t.target)+'\n');
+						buf.append("-").append(not?"~":"").append(st.label().toString(g.getTokenNames())).append("->").append(getStateString(t.target)).append('\n');
 					}
 				}
 				else if ( t instanceof AtomTransition ) {
 					AtomTransition a = (AtomTransition)t;
 					String label = a.toString();
 					if ( g!=null ) label = g.getTokenDisplayName(a.label);
-					buf.append("-"+label+"->"+ getStateString(t.target)+'\n');
+					buf.append("-").append(label).append("->").append(getStateString(t.target)).append('\n');
 				}
 				else {
-					buf.append("-"+t.toString()+"->"+ getStateString(t.target)+'\n');
+					buf.append("-").append(t.toString()).append("->").append(getStateString(t.target)).append('\n');
 				}
 			}
 		}
diff --git a/tool/src/org/antlr/v4/automata/ATNSerializer.java b/tool/src/org/antlr/v4/automata/ATNSerializer.java
index 64e7a0f71..5d727854b 100644
--- a/tool/src/org/antlr/v4/automata/ATNSerializer.java
+++ b/tool/src/org/antlr/v4/automata/ATNSerializer.java
@@ -200,7 +200,7 @@ public class ATNSerializer {
 		int p = 0;
 		int grammarType = ATNSimulator.toInt(data[p++]);
 		int maxType = ATNSimulator.toInt(data[p++]);
-		buf.append("max type "+maxType+"\n");
+		buf.append("max type ").append(maxType).append("\n");
 		int nstates = ATNSimulator.toInt(data[p++]);
 		for (int i=1; i<=nstates; i++) {
 			int stype = ATNSimulator.toInt(data[p++]);
@@ -211,9 +211,9 @@ public class ATNSerializer {
 				int loopBackStateNumber = ATNSimulator.toInt(data[p++]);
 				arg = " "+loopBackStateNumber;
 			}
-			buf.append((i - 1) + ":" +
-					   ATNState.serializationNames.get(stype) + " "+
-					   ruleIndex + arg + "\n");
+			buf.append(i - 1).append(":")
+				.append(ATNState.serializationNames.get(stype)).append(" ")
+				.append(ruleIndex).append(arg).append("\n");
 		}
 		int nrules = ATNSimulator.toInt(data[p++]);
 		for (int i=0; i<nrules; i++) {
@@ -221,24 +221,24 @@ public class ATNSerializer {
             if ( g.isLexer() ) {
                 int arg1 = ATNSimulator.toInt(data[p++]);
                 int arg2 = ATNSimulator.toInt(data[p++]);
-                buf.append("rule "+i+":"+s+" "+arg1+","+arg2+'\n');
+                buf.append("rule ").append(i).append(":").append(s).append(" ").append(arg1).append(",").append(arg2).append('\n');
             }
             else {
-                buf.append("rule "+i+":"+s+'\n');
+                buf.append("rule ").append(i).append(":").append(s).append('\n');
             }
 		}
 		int nmodes = ATNSimulator.toInt(data[p++]);
 		for (int i=0; i<nmodes; i++) {
 			int s = ATNSimulator.toInt(data[p++]);
-			buf.append("mode "+i+":"+s+'\n');
+			buf.append("mode ").append(i).append(":").append(s).append('\n');
 		}
 		int nsets = ATNSimulator.toInt(data[p++]);
 		for (int i=1; i<=nsets; i++) {
 			int nintervals = ATNSimulator.toInt(data[p++]);
-			buf.append((i-1)+":");
+			buf.append(i-1).append(":");
 			for (int j=1; j<=nintervals; j++) {
 				if ( j>1 ) buf.append(", ");
-				buf.append(getTokenName(ATNSimulator.toInt(data[p]))+".."+getTokenName(ATNSimulator.toInt(data[p + 1])));
+				buf.append(getTokenName(ATNSimulator.toInt(data[p]))).append("..").append(getTokenName(ATNSimulator.toInt(data[p + 1])));
 				p += 2;
 			}
 			buf.append("\n");
@@ -251,17 +251,17 @@ public class ATNSerializer {
 			int arg1 = ATNSimulator.toInt(data[p + 3]);
 			int arg2 = ATNSimulator.toInt(data[p + 4]);
 			int arg3 = ATNSimulator.toInt(data[p + 5]);
-			buf.append(src+"->"+trg+
-					   " "+Transition.serializationNames.get(ttype)+
-					   " "+arg1+","+arg2+","+arg3+
-					   "\n");
+			buf.append(src).append("->").append(trg)
+				.append(" ").append(Transition.serializationNames.get(ttype))
+				.append(" ").append(arg1).append(",").append(arg2).append(",").append(arg3)
+				.append("\n");
 			p += 6;
 		}
 		int ndecisions = ATNSimulator.toInt(data[p++]);
 		for (int i=1; i<=ndecisions; i++) {
 			int s = ATNSimulator.toInt(data[p++]);
 			int isGreedy = ATNSimulator.toInt(data[p++]);
-			buf.append((i-1)+":"+s+" "+isGreedy+"\n");
+			buf.append(i-1).append(":").append(s).append(" ").append(isGreedy).append("\n");
 		}
 		return buf.toString();
 	}
diff --git a/tool/src/org/antlr/v4/parse/ATNBuilder.g b/tool/src/org/antlr/v4/parse/ATNBuilder.g
index 8ab10147c..82060a03b 100644
--- a/tool/src/org/antlr/v4/parse/ATNBuilder.g
+++ b/tool/src/org/antlr/v4/parse/ATNBuilder.g
@@ -106,7 +106,7 @@ alternative returns [ATNFactory.Handle p]
 
 lexerCommands returns [ATNFactory.Handle p]
 @init {StringBuilder cmds = new StringBuilder();}
-    :   (c=lexerCommand {cmds.append($c.cmd+" ");})+
+    :   (c=lexerCommand {cmds.append($c.cmd).append(' ');})+
         {
         $p = factory.action(cmds.toString());
         }
diff --git a/tool/src/org/antlr/v4/parse/ActionSplitter.g b/tool/src/org/antlr/v4/parse/ActionSplitter.g
index 0776b0de9..5f1e437d6 100644
--- a/tool/src/org/antlr/v4/parse/ActionSplitter.g
+++ b/tool/src/org/antlr/v4/parse/ActionSplitter.g
@@ -82,7 +82,7 @@ TEXT
 @after {delegate.text(buf.toString());}
 	:	(	c=~('\\'| '$') {buf.append((char)$c);}
 		|	'\\$' {buf.append("$");}
-		|	'\\' c=~('$') {buf.append("\\"+(char)$c);}
+		|	'\\' c=~('$') {buf.append('\\').append((char)$c);}
 		)+
 	;
 
diff --git a/tool/src/org/antlr/v4/tool/Rule.java b/tool/src/org/antlr/v4/tool/Rule.java
index 2bdc12f53..e029c493f 100644
--- a/tool/src/org/antlr/v4/tool/Rule.java
+++ b/tool/src/org/antlr/v4/tool/Rule.java
@@ -346,9 +346,9 @@ public class Rule implements AttributeResolver {
 	@Override
     public String toString() {
 		StringBuilder buf = new StringBuilder();
-		buf.append("Rule{name="+name);
-		if ( args!=null ) buf.append(", args=" + args);
-		if ( retvals!=null ) buf.append(", retvals=" + retvals);
+		buf.append("Rule{name=").append(name);
+		if ( args!=null ) buf.append(", args=").append(args);
+		if ( retvals!=null ) buf.append(", retvals=").append(retvals);
 		buf.append("}");
 		return buf.toString();
     }