Because of the role of constructors in the language, fewer modifiers are meaningful than for methods:

• Access modifiers: public, protected, and private
• Annotations

The ConstructorAccess example searches for constructors in a given class with the specified access modifier. It also displays whether the constructor is synthetic (compiler-generated) or of variable arity.

/*
 * Copyright (c) 1995 - 2008 Sun Microsystems, Inc.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *   - Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 *   - Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *
 *   - Neither the name of Sun Microsystems nor the names of its
 *     contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */ 

import java.lang.reflect.Constructor;
import java.lang.reflect.Modifier;
import java.lang.reflect.Type;
import static java.lang.System.out;

public class ConstructorAccess {
    public static void main(String... args) {
	try {
	    Class<?> c = Class.forName(args[0]);
	    Constructor[] allConstructors = c.getDeclaredConstructors();
	    for (Constructor ctor : allConstructors) {
		int searchMod = modifierFromString(args[1]);
		int mods = accessModifiers(ctor.getModifiers());
		if (searchMod == mods) {
		    out.format("%s%n", ctor.toGenericString());
		    out.format("  [ synthetic=%-5b var_args=%-5b ]%n",
			       ctor.isSynthetic(), ctor.isVarArgs());
		}
	    }

        // production code should handle this exception more gracefully
	} catch (ClassNotFoundException x) {
	    x.printStackTrace();
	}
    }

    private static int accessModifiers(int m) {
	return m & (Modifier.PUBLIC | Modifier.PRIVATE | Modifier.PROTECTED);
    }

    private static int modifierFromString(String s) {
	if ("public".equals(s))               return Modifier.PUBLIC;
	else if ("protected".equals(s))       return Modifier.PROTECTED;
	else if ("private".equals(s))         return Modifier.PRIVATE;
	else if ("package-private".equals(s)) return 0;
	else return -1;
    }
}

There is not an explicit Modifier constant which corresponds to "package-private" access, so it is necessary to check for the absence of all three access modifiers to identify a package-private constructor.

This output shows the private constructors in java.io.File:

$ java ConstructorAccess java.io.File private
private java.io.File(java.lang.String,int)
  [ synthetic=false var_args=false ]
private java.io.File(java.lang.String,java.io.File)
  [ synthetic=false var_args=false ]

Synthetic constructors are rare; however the SyntheticConstructor example illustrates a typical situation where this may occur:

/*
 * Copyright (c) 1995 - 2008 Sun Microsystems, Inc.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *   - Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 *   - Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *
 *   - Neither the name of Sun Microsystems nor the names of its
 *     contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */ 

public class SyntheticConstructor {
    private SyntheticConstructor() {}
    class Inner {
	// Compiler will generate a synthetic constructor since
	// SyntheticConstructor() is private.
	Inner() { new SyntheticConstructor(); }
    }
}

$ java ConstructorAccess SyntheticConstructor package-private
SyntheticConstructor(SyntheticConstructor$1)
  [ synthetic=true  var_args=false ]

Since the inner class's constructor references the private constructor of the enclosing class, the compiler must generate a package-private constructor. The parameter type SyntheticConstructor$1 is arbitrary and dependent on the compiler implementation. Code which depends on the presence of any synthetic or non-public class members may not be portable.

Constructors implement java.lang.reflect.AnnotatedElement, which provides methods to retrieve runtime annotations with java.lang.annotation.RetentionPolicy.RUNTIME. For an example of obtaining annotations see the Examining Class Modifiers and Types section.