Convert a wrapper array to primitive array in Java

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

 

Step 1: Write a function that return a primitive type equivalent to the given wrapper type.

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

static {
	WRAPPER_TO_PRIMITIVE = new LinkedHashMap<>();

	WRAPPER_TO_PRIMITIVE.put(Byte.class, byte.class);
	WRAPPER_TO_PRIMITIVE.put(Short.class, short.class);
	WRAPPER_TO_PRIMITIVE.put(Integer.class, int.class);
	WRAPPER_TO_PRIMITIVE.put(Long.class, long.class);
	WRAPPER_TO_PRIMITIVE.put(Float.class, float.class);
	WRAPPER_TO_PRIMITIVE.put(Double.class, double.class);
	WRAPPER_TO_PRIMITIVE.put(Boolean.class, boolean.class);
	WRAPPER_TO_PRIMITIVE.put(Character.class, char.class);
}

public static Class<?> getPrimitiveType(final Class<?> wrapperType) {
	final Class<?> primitiveType = WRAPPER_TO_PRIMITIVE.get(wrapperType);

	if (primitiveType == null) {
		throw new IllegalArgumentException("Given type is not a wrapper type");
	}

	return primitiveType;
}

Step 2: Get the component type of wrapper array.

Class<?> wrapperArrayClazz = wrapperArray.getClass();
Class<?> wrapperArrayComponentType = wrapperArrayClazz.getComponentType();

Step 3: Find the equivalent primitive type from the wrapper array component type.

Class<?> primitiveType = getPrimitiveType(wrapperArrayComponentType);

Step 4: Define primitive array and copy the elements one by one.

int length = Array.getLength(wrapperArray);
Object primitiveArray = Array.newInstance(primitiveType, length);
for (int i = 0; i < length; i++) {
	Object ele = Array.get(wrapperArray, i);
	Array.set(primitiveArray, i, ele);
}

Find the below working application.

 

ArrayWrapperToPrimitiveDemo.java

package com.sample.app.arrays;

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

public class ArrayWrapperToPrimitiveDemo {

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

	static {
		WRAPPER_TO_PRIMITIVE = new LinkedHashMap<>();

		WRAPPER_TO_PRIMITIVE.put(Byte.class, byte.class);
		WRAPPER_TO_PRIMITIVE.put(Short.class, short.class);
		WRAPPER_TO_PRIMITIVE.put(Integer.class, int.class);
		WRAPPER_TO_PRIMITIVE.put(Long.class, long.class);
		WRAPPER_TO_PRIMITIVE.put(Float.class, float.class);
		WRAPPER_TO_PRIMITIVE.put(Double.class, double.class);
		WRAPPER_TO_PRIMITIVE.put(Boolean.class, boolean.class);
		WRAPPER_TO_PRIMITIVE.put(Character.class, char.class);
	}

	public static Class<?> getPrimitiveType(final Class<?> wrapperType) {
		final Class<?> primitiveType = WRAPPER_TO_PRIMITIVE.get(wrapperType);

		if (primitiveType == null) {
			throw new IllegalArgumentException("Given type is not a wrapper type");
		}

		return primitiveType;
	}

	public static Object toPrimitiveArray(final Object wrapperArray) {

		if (wrapperArray == null) {
			throw new IllegalArgumentException("Wrapper array cannot be null");
		}

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

		final Class<?> wrapperArrayComponentType = wrapperArrayClazz.getComponentType();
		final Class<?> primitiveType = getPrimitiveType(wrapperArrayComponentType);
		final int length = Array.getLength(wrapperArray);

		final Object primitiveArray = Array.newInstance(primitiveType, length);
		for (int i = 0; i < length; i++) {
			final Object ele = Array.get(wrapperArray, i);
			Array.set(primitiveArray, i, ele);
		}
		return primitiveArray;
	}

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

		int[] primesPrimitiveArray = (int[]) toPrimitiveArray(primes);

		for (int i : primesPrimitiveArray) {
			System.out.println(i);
		}
	}
}

Output

2
3
5
7
11

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