Convert a primitive array to wrapper array in Java

Write a program to convert the primitive array to wrapper array in Java. For example, for the int[] array, you should return Integer[].

 

Step 1: Let’s define a map, to get the wrapper type equivalent to the given primitive type.

private static final Map<Class<?>, Class<?>> PRIMITIVES_TO_WRAPPERS;

static {
	PRIMITIVES_TO_WRAPPERS = new LinkedHashMap<>();
	PRIMITIVES_TO_WRAPPERS.put(boolean.class, Boolean.class);
	PRIMITIVES_TO_WRAPPERS.put(byte.class, Byte.class);
	PRIMITIVES_TO_WRAPPERS.put(char.class, Character.class);
	PRIMITIVES_TO_WRAPPERS.put(double.class, Double.class);
	PRIMITIVES_TO_WRAPPERS.put(float.class, Float.class);
	PRIMITIVES_TO_WRAPPERS.put(int.class, Integer.class);
	PRIMITIVES_TO_WRAPPERS.put(long.class, Long.class);
	PRIMITIVES_TO_WRAPPERS.put(short.class, Short.class);
	PRIMITIVES_TO_WRAPPERS.put(void.class, Void.class);
}

Step 2: Define a method that return a wrapper type equivalent to the given primitive type.

public static Class<?> getWrapperType(Class<?> primitiveType) {
	if (primitiveType.isPrimitive()) {
		return PRIMITIVES_TO_WRAPPERS.get(primitiveType);
	}
	throw new IllegalArgumentException("Given type is not primitive");
}

Step 3: Get the component type of given input array.

Class<?> clazz = primitiveArray.getClass();
Class<?> componentType = clazz.getComponentType();

Step 4: Define new array using the input array component type and copy the elements from input array to this wrapper array.

int inputArrayLength = Array.getLength(primitiveArray);
Object[] arr = (Object[]) Array.newInstance(getWrapperType(componentType), inputArrayLength);

for (int i = 0; i < inputArrayLength; i++) {
	arr[i] = Array.get(primitiveArray, i);
}

Find the below working application.

ArrayPrimitiveToWrapperDemo.java

package com.sample.app.arrays;

import java.lang.reflect.Array;
import java.util.LinkedHashMap;
import java.util.Map;

public class ArrayPrimitiveToWrapperDemo {

	private static final Map<Class<?>, Class<?>> PRIMITIVES_TO_WRAPPERS;

	static {
		PRIMITIVES_TO_WRAPPERS = new LinkedHashMap<>();
		PRIMITIVES_TO_WRAPPERS.put(boolean.class, Boolean.class);
		PRIMITIVES_TO_WRAPPERS.put(byte.class, Byte.class);
		PRIMITIVES_TO_WRAPPERS.put(char.class, Character.class);
		PRIMITIVES_TO_WRAPPERS.put(double.class, Double.class);
		PRIMITIVES_TO_WRAPPERS.put(float.class, Float.class);
		PRIMITIVES_TO_WRAPPERS.put(int.class, Integer.class);
		PRIMITIVES_TO_WRAPPERS.put(long.class, Long.class);
		PRIMITIVES_TO_WRAPPERS.put(short.class, Short.class);
		PRIMITIVES_TO_WRAPPERS.put(void.class, Void.class);
	}

	public static Class<?> getWrapperType(Class<?> primitiveType) {
		if (primitiveType.isPrimitive()) {
			return PRIMITIVES_TO_WRAPPERS.get(primitiveType);
		}
		throw new IllegalArgumentException("Given type is not primitive");
	}

	public static Object[] toWrapperArray(final Object primitiveArray) {

		if (primitiveArray == null) {
			throw new IllegalArgumentException("primitiveArray can't null");
		}

		final Class<?> clazz = primitiveArray.getClass();
		if (!clazz.isArray()) {
			throw new IllegalArgumentException("input is not an array");
		}

		final Class<?> componentType = clazz.getComponentType();
		if (!componentType.isPrimitive()) {
			throw new IllegalArgumentException("Input is not a primitive array");
		}

		final int inputArrayLength = Array.getLength(primitiveArray);

		final Object[] arr = (Object[]) Array.newInstance(getWrapperType(componentType), inputArrayLength);

		for (int i = 0; i < inputArrayLength; i++) {
			arr[i] = Array.get(primitiveArray, i);
		}
		return arr;
	}

	public static void main(String[] args) {
		final int[] primes = new int[] { 2, 3, 5, 7, 11 };

		final Integer[] primesWrapperArray = (Integer[]) toWrapperArray(primes);

		for (Integer i : primesWrapperArray) {
			System.out.println(i);
		}
	}

}

Output

2
3
5
7
11

 

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