How to get generic types of map in Java?

Below snippet prints generic type of a field.

public static void printGenericType(Field field) {
 ParameterizedType genericType = (ParameterizedType) field.getGenericType();

 int lengthOfArguments = genericType.getActualTypeArguments().length;

 System.out.println(field.getName() + " has " + lengthOfArguments + " arguments");
 for (int i = 0; i < lengthOfArguments; i++) {
  Class<?> typeArgument = (Class<?>) genericType.getActualTypeArguments()[i];
  System.out.println("\t" + i + "th argument : " + typeArgument);
 }

 System.out.println();
}

For example DemoCollection define two lists and one map.

public class DemoCollection {
 private List<String> strList;
 private List<Double> doubleList;
 private Map<String, Integer> myMap;
}

Below snippet prints generic types of the map "myMap".

Field field = DemoCollection.class.getDeclaredField("myMap");

printGenericType(field);

DemoCollection.java

package com.sample.app;

import java.util.List;
import java.util.Map;

public class DemoCollection {
 private List<String> strList;
 private List<Double> doubleList;
 private Map<String, Integer> myMap;
}

App.java

package com.sample.app;

import java.lang.reflect.Field;
import java.lang.reflect.ParameterizedType;

public class App {

 public static void printGenericTypes(Class<?> clazz) {
  Field[] fields = clazz.getDeclaredFields();

  for (Field field : fields) {

   printGenericType(field);
  }

 }

 public static void printGenericType(Field field) {
  ParameterizedType genericType = (ParameterizedType) field.getGenericType();

  int lengthOfArguments = genericType.getActualTypeArguments().length;

  System.out.println(field.getName() + " has " + lengthOfArguments + " arguments");
  for (int i = 0; i < lengthOfArguments; i++) {
   Class<?> typeArgument = (Class<?>) genericType.getActualTypeArguments()[i];
   System.out.println("\t" + i + "th argument : " + typeArgument);
  }

  System.out.println();
 }

 public static void main(String... args) throws Exception {
  printGenericTypes(DemoCollection.class);

  System.out.println("***************************");
  Field field = DemoCollection.class.getDeclaredField("myMap");
  printGenericType(field);
 }

}

Output

strList has 1 arguments
 0th argument : class java.lang.String

doubleList has 1 arguments
 0th argument : class java.lang.Double

myMap has 2 arguments
 0th argument : class java.lang.String
 1th argument : class java.lang.Integer

***************************
myMap has 2 arguments
 0th argument : class java.lang.String
 1th argument : class java.lang.Integer

You may like

Miscellaneous

Interview Questions

Programming Questions

How to get sub array or part of array

Get file name by removing extension

System getProperties vs getenv

What are -Xms and -Xmx parameters while launching java application?

Get Generic type of a list