Here you can find the source of isPrimitiveWrapper(Class> clazz)
public static boolean isPrimitiveWrapper(Class<?> clazz)
//package com.java2s; //License from project: Apache License import java.util.*; public class Main { private static final Set<Class<?>> primitiveWrapperTypes = new HashSet<>(8); public static boolean isPrimitiveWrapper(Class<?> clazz) { return primitiveWrapperTypes.contains(clazz); }//from w w w.j a va 2s . c o m }