How many fields can a Java record hold?

Question

What is the maximum number of properties (“record components”, technically) defined in a Java record?

I read the specification, JEP 395: Records. No mention of a limit.

Answer 1

254

Some trial-and-error found 254 to be the limit.

Using 255 fields results in an error (too many parameters) in:

• IntelliJ 2023.2 with Java 21
• javac from JDK 20.0.2

Example code:

package work.basil.example.codegen;

public record MaxRec (
        String x001 ,
        String x002 ,
        String x003 ,
        String x004 ,
        String x005 ,
        String x006 ,
        String x007 ,
        String x008 ,
        String x009 ,
        String x010 ,
        String x011 ,
        String x012 ,
        String x013 ,
        String x014 ,
        String x015 ,
        String x016 ,
        String x017 ,
        String x018 ,
        String x019 ,
        String x020 ,
        String x021 ,
        String x022 ,
        String x023 ,
        String x024 ,
        String x025 ,
        String x026 ,
        String x027 ,
        String x028 ,
        String x029 ,
        String x030 ,
        String x031 ,
        String x032 ,
        String x033 ,
        String x034 ,
        String x035 ,
        String x036 ,
        String x037 ,
        String x038 ,
        String x039 ,
        String x040 ,
        String x041 ,
        String x042 ,
        String x043 ,
        String x044 ,
        String x045 ,
        String x046 ,
        String x047 ,
        String x048 ,
        String x049 ,
        String x050 ,
        String x051 ,
        String x052 ,
        String x053 ,
        String x054 ,
        String x055 ,
        String x056 ,
        String x057 ,
        String x058 ,
        String x059 ,
        String x060 ,
        String x061 ,
        String x062 ,
        String x063 ,
        String x064 ,
        String x065 ,
        String x066 ,
        String x067 ,
        String x068 ,
        String x069 ,
        String x070 ,
        String x071 ,
        String x072 ,
        String x073 ,
        String x074 ,
        String x075 ,
        String x076 ,
        String x077 ,
        String x078 ,
        String x079 ,
        String x080 ,
        String x081 ,
        String x082 ,
        String x083 ,
        String x084 ,
        String x085 ,
        String x086 ,
        String x087 ,
        String x088 ,
        String x089 ,
        String x090 ,
        String x091 ,
        String x092 ,
        String x093 ,
        String x094 ,
        String x095 ,
        String x096 ,
        String x097 ,
        String x098 ,
        String x099 ,
        String x100 ,
        String x101 ,
        String x102 ,
        String x103 ,
        String x104 ,
        String x105 ,
        String x106 ,
        String x107 ,
        String x108 ,
        String x109 ,
        String x110 ,
        String x111 ,
        String x112 ,
        String x113 ,
        String x114 ,
        String x115 ,
        String x116 ,
        String x117 ,
        String x118 ,
        String x119 ,
        String x120 ,
        String x121 ,
        String x122 ,
        String x123 ,
        String x124 ,
        String x125 ,
        String x126 ,
        String x127 ,
        String x128 ,
        String x129 ,
        String x130 ,
        String x131 ,
        String x132 ,
        String x133 ,
        String x134 ,
        String x135 ,
        String x136 ,
        String x137 ,
        String x138 ,
        String x139 ,
        String x140 ,
        String x141 ,
        String x142 ,
        String x143 ,
        String x144 ,
        String x145 ,
        String x146 ,
        String x147 ,
        String x148 ,
        String x149 ,
        String x150 ,
        String x151 ,
        String x152 ,
        String x153 ,
        String x154 ,
        String x155 ,
        String x156 ,
        String x157 ,
        String x158 ,
        String x159 ,
        String x160 ,
        String x161 ,
        String x162 ,
        String x163 ,
        String x164 ,
        String x165 ,
        String x166 ,
        String x167 ,
        String x168 ,
        String x169 ,
        String x170 ,
        String x171 ,
        String x172 ,
        String x173 ,
        String x174 ,
        String x175 ,
        String x176 ,
        String x177 ,
        String x178 ,
        String x179 ,
        String x180 ,
        String x181 ,
        String x182 ,
        String x183 ,
        String x184 ,
        String x185 ,
        String x186 ,
        String x187 ,
        String x188 ,
        String x189 ,
        String x190 ,
        String x191 ,
        String x192 ,
        String x193 ,
        String x194 ,
        String x195 ,
        String x196 ,
        String x197 ,
        String x198 ,
        String x199 ,
        String x200 ,
        String x201 ,
        String x202 ,
        String x203 ,
        String x204 ,
        String x205 ,
        String x206 ,
        String x207 ,
        String x208 ,
        String x209 ,
        String x210 ,
        String x211 ,
        String x212 ,
        String x213 ,
        String x214 ,
        String x215 ,
        String x216 ,
        String x217 ,
        String x218 ,
        String x219 ,
        String x220 ,
        String x221 ,
        String x222 ,
        String x223 ,
        String x224 ,
        String x225 ,
        String x226 ,
        String x227 ,
        String x228 ,
        String x229 ,
        String x230 ,
        String x231 ,
        String x232 ,
        String x233 ,
        String x234 ,
        String x235 ,
        String x236 ,
        String x237 ,
        String x238 ,
        String x239 ,
        String x240 ,
        String x241 ,
        String x242 ,
        String x243 ,
        String x244 ,
        String x245 ,
        String x246 ,
        String x247 ,
        String x248 ,
        String x249 ,
        String x250 ,
        String x251 ,
        String x252 ,
        String x253 ,
        String x254
        // , String x255  // Error: too many parameters
) {}

---

By the way, for fun, here is the code used to generate the above code.

This code generates Java source code. That source code appears on your console. Copy/paste that source code into a text file. Name that file MaxRec.java. Compile that file. See error appear.

package work.basil.example.codegen;

import java.util.List;
import java.util.stream.IntStream;

public class MaxArgsInRecord
{
    public static void main ( String[] args )
    {
        System.out.println ( "public record MaxRec (" );
        int countProperties = 255;
        List < String > fields =
                IntStream
                        .rangeClosed ( 1 , countProperties )
                        .mapToObj (
                                ( int i ) -> "   String x" + String.format ( "%03d" , i )
                        )
                        .toList ( );
        System.out.println ( String.join ( " ,\n" , fields ) );
        System.out.println ( ") {}" );
    }
}

Answer 2

255 - 1 = 254

Due to the limit on method descriptor length, the maximum number of parameters a method can define is 255. Including the this, since a record constructor is non-static, that leaves 254.

See Java Virtual Machine Specification, 4.3.3. Method Descriptors

I believe a record must have at least one constructor that takes all properties as individual parameters, so this would effectively limit the number of record components.