java.lang.reflect.Method＃getModifiers返回有效范围外的标志？

Question

The following code:

Class.forName("java.lang.String")
     .getDeclaredMethods
     .find(_.getName == "join")
     .get
     .getModifiers & ~(java.lang.reflect.Modifier.methodModifiers())

Evaluates to 128 . It seems to me that it should evaluate to 0 , because every modifier that's attached to the java.lang.String#join method should be within the set of java.lang.reflect.Modifier.methodModifiers() .

Looking at the constants in java.lang.reflect.Modifier , it seems that 128 corresponds to the modifier bit java.lang.reflect.Modifier.TRANSIENT . How can a method end up being flagged as transient ?

Answer 1

Brief Explanation

There are two flags with the value 0x80 (128), VARARGS and TRANSIENT, as per the answer here , so the method is actually a varargs method.

The JavaDoc confirm that this method is varargs, so the flag makes sense

Worked example

import java.lang.reflect.Field;
import java.lang.reflect.Modifier;

class TestClass {
  public static void main(final String... args) throws Throwable{
    int methodModifiers = Class.forName("java.lang.String")
        .getDeclaredMethod("join", CharSequence.class, CharSequence[].class)
        .getModifiers();

    Field varargsField = Class.forName("java.lang.reflect.Modifier")
        .getDeclaredField("VARARGS");
    varargsField.setAccessible(true);

    int varargsF = varargsField.getInt(null);
    int staticF = Modifier.STATIC;
    int publicF = Modifier.PUBLIC;

    if (methodModifiers == publicF + staticF + varargsF) {
      System.out.println("Correct");
    } else {
      System.out.println("Wrong");
    }
  }
}