Constructor Lookup

A reflected constructor can create an object when the parameter types are known.

ConstructorLookup.java

import java.lang.reflect.Constructor;

public class ConstructorLookup {
    static class Person {
        private final String name;
        private final int age;

        Person(String name, int age) {
            this.name = name;
            this.age = age;
        }

        String label() {
            return name + ":" + age;
        }
    }

    public static void main(String[] args) throws Exception {
        int age = ;
        Constructor<Person> constructor =
                Person.class.getDeclaredConstructor(String.class, int.class);
        Person person = constructor.newInstance("Ada", age);

        System.out.println("person=" + person.label());
    }
}

import java.lang.reflect.Constructor;

public class ConstructorLookup {
    static class Person {
        private final String name;
        private final int age;

        Person(String name, int age) {
            this.name = name;
            this.age = age;
        }

        String label() {
            return name + ":" + age;
        }
    }

    public static void main(String[] args) throws Exception {
        int age = ;
        Constructor<Person> constructor =
                Person.class.getDeclaredConstructor(String.class, int.class);
        Person person = constructor.newInstance("Ada", age);

        System.out.println("person=" + person.label());
    }
}

import java.lang.reflect.Constructor;

public class ConstructorLookup {
    static class Person {
        private final String name;
        private final int age;

        Person(String name, int age) {
            this.name = name;
            this.age = age;
        }

        String label() {
            return name + ":" + age;
        }
    }

    public static void main(String[] args) throws Exception {
        int age = ;
        Constructor<Person> constructor =
                Person.class.getDeclaredConstructor(String.class, int.class);
        Person person = constructor.newInstance("Ada", age);

        System.out.println("person=" + person.label());
    }
}

constructor metadata A Constructor object describes how to create a class instance.

newInstance Calling newInstance runs the constructor with the supplied arguments.