src/java.base/share/classes/java/lang/reflect/Executable.java

*** 26,35 ****
--- 26,36 ----
  package java.lang.reflect;
  
  import java.lang.annotation.*;
  import java.util.Map;
  import java.util.Objects;
+ import java.util.StringJoiner;
  
  import jdk.internal.misc.SharedSecrets;
  import sun.reflect.annotation.AnnotationParser;
  import sun.reflect.annotation.AnnotationSupport;
  import sun.reflect.annotation.TypeAnnotationParser;
*** 84,102 ****
                 SharedSecrets.getJavaLangAccess().
                 getConstantPool(getDeclaringClass()),
                 getDeclaringClass());
      }
  
-     void separateWithCommas(Class<?>[] types, StringBuilder sb) {
-         for (int j = 0; j < types.length; j++) {
-             sb.append(types[j].getTypeName());
-             if (j < (types.length - 1))
-                 sb.append(",");
-         }
- 
-     }
- 
      void printModifiersIfNonzero(StringBuilder sb, int mask, boolean isDefault) {
          int mod = getModifiers() & mask;
  
          if (mod != 0 && !isDefault) {
              sb.append(Modifier.toString(mod)).append(' ');
--- 85,94 ----
*** 119,135 ****
          try {
              StringBuilder sb = new StringBuilder();
  
              printModifiersIfNonzero(sb, modifierMask, isDefault);
              specificToStringHeader(sb);
  
-             sb.append('(');
-             separateWithCommas(parameterTypes, sb);
-             sb.append(')');
              if (exceptionTypes.length > 0) {
!                 sb.append(" throws ");
!                 separateWithCommas(exceptionTypes, sb);
              }
              return sb.toString();
          } catch (Exception e) {
              return "<" + e + ">";
          }
--- 111,133 ----
          try {
              StringBuilder sb = new StringBuilder();
  
              printModifiersIfNonzero(sb, modifierMask, isDefault);
              specificToStringHeader(sb);
+             StringJoiner sj = new StringJoiner(",", "(", ")");
+             sj.setEmptyValue("()");
+             for (Class<?> parameterType : parameterTypes) {
+                 sj.add(parameterType.getTypeName());
+             }
+             sb.append(sj.toString());
  
              if (exceptionTypes.length > 0) {
!                 StringJoiner joiner = new StringJoiner(",", "throws ", "");
!                 for (Class<?> exceptionType : exceptionTypes) {
!                     joiner.add(exceptionType.getTypeName());
!                 }
!                 sb.append(joiner.toString());
              }
              return sb.toString();
          } catch (Exception e) {
              return "<" + e + ">";
          }
*** 147,192 ****
  
              printModifiersIfNonzero(sb, modifierMask, isDefault);
  
              TypeVariable<?>[] typeparms = getTypeParameters();
              if (typeparms.length > 0) {
!                 boolean first = true;
!                 sb.append('<');
                  for(TypeVariable<?> typeparm: typeparms) {
!                     if (!first)
!                         sb.append(',');
!                     // Class objects can't occur here; no need to test
!                     // and call Class.getName().
!                     sb.append(typeparm.toString());
!                     first = false;
                  }
!                 sb.append("> ");
              }
  
              specificToGenericStringHeader(sb);
  
!             sb.append('(');
              Type[] params = getGenericParameterTypes();
              for (int j = 0; j < params.length; j++) {
                  String param = params[j].getTypeName();
                  if (isVarArgs() && (j == params.length - 1)) // replace T[] with T...
                      param = param.replaceFirst("\\[\\]$", "...");
!                 sb.append(param);
!                 if (j < (params.length - 1))
!                     sb.append(',');
!             }
!             sb.append(')');
!             Type[] exceptions = getGenericExceptionTypes();
!             if (exceptions.length > 0) {
!                 sb.append(" throws ");
!                 for (int k = 0; k < exceptions.length; k++) {
!                     sb.append((exceptions[k] instanceof Class)?
!                               ((Class)exceptions[k]).getName():
!                               exceptions[k].toString());
!                     if (k < (exceptions.length - 1))
!                         sb.append(',');
                  }
              }
              return sb.toString();
          } catch (Exception e) {
              return "<" + e + ">";
          }
--- 145,182 ----
  
              printModifiersIfNonzero(sb, modifierMask, isDefault);
  
              TypeVariable<?>[] typeparms = getTypeParameters();
              if (typeparms.length > 0) {
!                 StringJoiner sj = new StringJoiner(",", "<", "> ");
                  for(TypeVariable<?> typeparm: typeparms) { 
!                     sj.add(typeparm.getTypeName());
                  }
!                 sb.append(sj.toString());
              }
  
              specificToGenericStringHeader(sb);
  
!             StringJoiner sj = new StringJoiner(",", "(", ")");
!             sj.setEmptyValue("()");
! 
              Type[] params = getGenericParameterTypes();
              for (int j = 0; j < params.length; j++) {
                  String param = params[j].getTypeName();
                  if (isVarArgs() && (j == params.length - 1)) // replace T[] with T...
                      param = param.replaceFirst("\\[\\]$", "...");
!                 sj.add(param);
!             }
!             sb.append(sj.toString());
! 
!             Type[] exceptionTypes = getGenericExceptionTypes();
!             if (exceptionTypes.length > 0) {
!                 StringJoiner joiner = new StringJoiner(",", " throws ", "");
!                 for (Type exceptionType : exceptionTypes) {
!                     joiner.add(exceptionType.getTypeName());
                  }
+                 sb.append(joiner.toString());
              }
              return sb.toString();
          } catch (Exception e) {
              return "<" + e + ">";
          }