diff --git a/src/main/java/com/google/api/generator/gapic/composer/samplecode/ExecutableSampleComposer.java b/src/main/java/com/google/api/generator/gapic/composer/samplecode/ExecutableSampleComposer.java
index 14e5571223..58bcd29110 100644
--- a/src/main/java/com/google/api/generator/gapic/composer/samplecode/ExecutableSampleComposer.java
+++ b/src/main/java/com/google/api/generator/gapic/composer/samplecode/ExecutableSampleComposer.java
@@ -14,7 +14,17 @@
 
 package com.google.api.generator.gapic.composer.samplecode;
 
-import com.google.api.generator.engine.ast.*;
+import com.google.api.generator.engine.ast.AssignmentExpr;
+import com.google.api.generator.engine.ast.ClassDefinition;
+import com.google.api.generator.engine.ast.Expr;
+import com.google.api.generator.engine.ast.ExprStatement;
+import com.google.api.generator.engine.ast.MethodDefinition;
+import com.google.api.generator.engine.ast.MethodInvocationExpr;
+import com.google.api.generator.engine.ast.ScopeNode;
+import com.google.api.generator.engine.ast.Statement;
+import com.google.api.generator.engine.ast.TypeNode;
+import com.google.api.generator.engine.ast.Variable;
+import com.google.api.generator.engine.ast.VariableExpr;
 import com.google.api.generator.gapic.utils.JavaStyle;
 import com.google.common.collect.ImmutableList;
 import java.util.ArrayList;
@@ -41,7 +51,7 @@ public static String createExecutableSample(ExecutableSample executableSample) {
             executableSample.getSampleBody()));
   }
 
-  static ClassDefinition composeExecutableSample(
+  private static ClassDefinition composeExecutableSample(
       String sampleMethodName,
       List<AssignmentExpr> sampleVariableAssignments,
       List<Statement> sampleBody) {
@@ -57,14 +67,14 @@ static ClassDefinition composeExecutableSample(
     return composeSampleClass(sampleClassName, mainMethod, sampleMethod);
   }
 
-  static List<VariableExpr> composeSampleMethodArgs(
+  private static List<VariableExpr> composeSampleMethodArgs(
       List<AssignmentExpr> sampleVariableAssignments) {
     return sampleVariableAssignments.stream()
         .map(v -> v.variableExpr().toBuilder().setIsDecl(true).build())
         .collect(Collectors.toList());
   }
 
-  static Statement composeInvokeMethodStatement(
+  private static Statement composeInvokeMethodStatement(
       String sampleMethodName, List<VariableExpr> sampleMethodArgs) {
     List<Expr> invokeArgs =
         sampleMethodArgs.stream()
@@ -77,7 +87,7 @@ static Statement composeInvokeMethodStatement(
             .build());
   }
 
-  static List<Statement> composeMainBody(
+  private static List<Statement> composeMainBody(
       List<AssignmentExpr> sampleVariableAssignments, Statement invokeMethod) {
     List<ExprStatement> setVariables =
         sampleVariableAssignments.stream()
@@ -88,7 +98,7 @@ static List<Statement> composeMainBody(
     return body;
   }
 
-  static ClassDefinition composeSampleClass(
+  private static ClassDefinition composeSampleClass(
       String sampleClassName, MethodDefinition mainMethod, MethodDefinition sampleMethod) {
     return ClassDefinition.builder()
         .setScope(ScopeNode.PUBLIC)
@@ -98,7 +108,7 @@ static ClassDefinition composeSampleClass(
         .build();
   }
 
-  static MethodDefinition composeMainMethod(List<Statement> mainBody) {
+  private static MethodDefinition composeMainMethod(List<Statement> mainBody) {
     return MethodDefinition.builder()
         .setScope(ScopeNode.PUBLIC)
         .setIsStatic(true)
@@ -115,7 +125,7 @@ static MethodDefinition composeMainMethod(List<Statement> mainBody) {
         .build();
   }
 
-  static MethodDefinition composeSampleMethod(
+  private static MethodDefinition composeSampleMethod(
       String sampleMethodName,
       List<VariableExpr> sampleMethodArgs,
       List<Statement> sampleMethodBody) {
diff --git a/src/main/java/com/google/api/generator/gapic/composer/samplecode/SampleUtil.java b/src/main/java/com/google/api/generator/gapic/composer/samplecode/SampleUtil.java
index 41520574c5..664e886cf3 100644
--- a/src/main/java/com/google/api/generator/gapic/composer/samplecode/SampleUtil.java
+++ b/src/main/java/com/google/api/generator/gapic/composer/samplecode/SampleUtil.java
@@ -14,14 +14,21 @@
 
 package com.google.api.generator.gapic.composer.samplecode;
 
-import com.google.api.generator.engine.ast.*;
+import com.google.api.client.util.Preconditions;
+import com.google.api.generator.engine.ast.Expr;
+import com.google.api.generator.engine.ast.MethodInvocationExpr;
+import com.google.api.generator.engine.ast.StringObjectValue;
+import com.google.api.generator.engine.ast.TypeNode;
+import com.google.api.generator.engine.ast.ValueExpr;
+import com.google.api.generator.engine.ast.VaporReference;
+import com.google.api.generator.engine.ast.VariableExpr;
 import com.google.api.generator.gapic.utils.JavaStyle;
 
 public class SampleUtil {
   public static String composeSampleMethodName(String clientName, String methodName) {
-    if (clientName.equals("") || methodName.equals("")) {
-      throw new IllegalArgumentException("clientName and methodName must exist");
-    }
+    Preconditions.checkArgument(
+        !clientName.isEmpty() && !methodName.isEmpty(),
+        "clientName and methodName must not be empty");
     return JavaStyle.toLowerCamelCase(clientName + JavaStyle.toUpperCamelCase(methodName));
   }
 
@@ -33,7 +40,7 @@ public static MethodInvocationExpr systemOutPrint(VariableExpr variableExpr) {
     return composeSystemOutPrint(variableExpr.toBuilder().setIsDecl(false).build());
   }
 
-  static MethodInvocationExpr composeSystemOutPrint(Expr content) {
+  private static MethodInvocationExpr composeSystemOutPrint(Expr content) {
     VaporReference out =
         VaporReference.builder()
             .setEnclosingClassNames("System")
diff --git a/src/test/java/com/google/api/generator/gapic/composer/samplecode/ExecutableSampleComposerTest.java b/src/test/java/com/google/api/generator/gapic/composer/samplecode/ExecutableSampleComposerTest.java
index 7fcccde74b..653842b147 100644
--- a/src/test/java/com/google/api/generator/gapic/composer/samplecode/ExecutableSampleComposerTest.java
+++ b/src/test/java/com/google/api/generator/gapic/composer/samplecode/ExecutableSampleComposerTest.java
@@ -16,7 +16,14 @@
 
 import static org.junit.Assert.assertEquals;
 
-import com.google.api.generator.engine.ast.*;
+import com.google.api.generator.engine.ast.AssignmentExpr;
+import com.google.api.generator.engine.ast.ExprStatement;
+import com.google.api.generator.engine.ast.Statement;
+import com.google.api.generator.engine.ast.StringObjectValue;
+import com.google.api.generator.engine.ast.TypeNode;
+import com.google.api.generator.engine.ast.ValueExpr;
+import com.google.api.generator.engine.ast.Variable;
+import com.google.api.generator.engine.ast.VariableExpr;
 import com.google.api.generator.testutils.LineFormatter;
 import com.google.common.collect.ImmutableList;
 import java.util.ArrayList;