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Java Reflection - Class.getDeclaredConstructor() Examples

Java Reflection Java Java API 

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Class:

java.lang.Class

java.lang.Objectjava.lang.Objectjava.lang.Classjava.lang.Classjava.io.SerializableSerializablejava.lang.reflect.GenericDeclarationGenericDeclarationjava.lang.reflect.TypeTypejava.lang.reflect.AnnotatedElementAnnotatedElementLogicBig

Method:

public Constructor<T> getDeclaredConstructor(Class<?>... parameterTypes)
                                      throws NoSuchMethodException, SecurityException
Parameters:
parameterTypes - the parameter array
Returns:
The Constructor object for the constructor with the specified parameter list


Examples


package com.logicbig.example.clazz;

import java.lang.reflect.Constructor;

public class GetDeclaredConstructorExample {

    public GetDeclaredConstructorExample() {
    }

    public GetDeclaredConstructorExample(int i) {
    }

    private GetDeclaredConstructorExample(String s) {
    }

    public static void main(String... args) throws NoSuchMethodException {
        Class<GetDeclaredConstructorExample> c = GetDeclaredConstructorExample.class;
        Constructor<GetDeclaredConstructorExample> cons = c.getDeclaredConstructor();
        System.out.println(cons);

        cons = c.getDeclaredConstructor(int.class);
        System.out.println(cons);

        cons = c.getDeclaredConstructor(String.class);
        System.out.println(cons);
    }

}

Output

public com.logicbig.example.clazz.GetDeclaredConstructorExample()
public com.logicbig.example.clazz.GetDeclaredConstructorExample(int)
private com.logicbig.example.clazz.GetDeclaredConstructorExample(java.lang.String)




Inner class's first parameter is of the outer class type (implicitly added during compilation).
See Also: Implicit Outer Class Parameter Tutorial 

package com.logicbig.example.clazz;

import java.lang.reflect.Constructor;
import java.util.Arrays;

public class GetDeclaredConstructorExample2 {

    public static void main(String... args) throws NoSuchMethodException {
        Class<MyClass.TheInnerClass> c = MyClass.TheInnerClass.class;
        Constructor<MyClass.TheInnerClass> cons = c.getDeclaredConstructor(MyClass.class, int.class);
        System.out.println(cons);
        System.out.println(cons.getName());
        System.out.println(Arrays.toString(cons.getParameters()));
    }

    private static class MyClass {
        private class TheInnerClass {
            private int i;

            private TheInnerClass(int i) {
                this.i = i;
            }
        }
    }
}

Output

private com.logicbig.example.clazz.GetDeclaredConstructorExample2$MyClass$TheInnerClass(com.logicbig.example.clazz.GetDeclaredConstructorExample2$MyClass,int)
com.logicbig.example.clazz.GetDeclaredConstructorExample2$MyClass$TheInnerClass
[com.logicbig.example.clazz.GetDeclaredConstructorExample2$MyClass arg0, int arg1]

See Also