Close

Java Reflection - Array.newInstance() Examples

Java Reflection Java Java API 

PreviousNext

Class:

java.lang.reflect.Array

java.lang.Objectjava.lang.Objectjava.lang.reflect.Arrayjava.lang.reflect.ArrayLogicBig

Methods:

public static Object newInstance(Class<?> componentType,
                                 int length)
                          throws NegativeArraySizeException

Creates a new array with the specified component type and length.

The number of dimensions of the new array must not exceed 255.



public static Object newInstance(Class<?> componentType,
                                 int... dimensions)
                          throws IllegalArgumentException,
                                 NegativeArraySizeException

Creates a new array with the specified component type and dimensions.

The number of dimensions of the new array must not exceed 255.


Examples


package com.logicbig.example.array;

import java.lang.reflect.Array;
import java.math.BigDecimal;
import java.math.BigInteger;
import java.util.Arrays;

public class NewInstanceExample {

    public static void main(String... args) {
        int len = 4;
        Object o = Array.newInstance(BigDecimal.class, len);
        for (int i = 0; i < len; i++) {
            Array.set(o, i, BigDecimal.valueOf(i));
        }
        System.out.println(Arrays.toString((Object[]) o));
    }
}

Output

[0, 1, 2, 3]




package com.logicbig.example.array;

import java.lang.reflect.Array;
import java.util.Arrays;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.stream.IntStream;

public class NewInstanceExample2 {

    public static void main(String... args) {
        List<String> list = Arrays.asList("one", "two", "three");
        String[] strings = toArray(list, String.class);
        System.out.println(Arrays.toString(strings));
    }

    public static  <T> T[] toArray(Collection<T> c, Class<T> type) {
        if (c == null) {
            return null;
        }
        Object o = Array.newInstance(type, c.size());
        Iterator<T> iterator = c.iterator();
        IntStream.range(0, c.size())
                 .forEach(i -> Array.set(o, i, iterator.next()));
        @SuppressWarnings("unchecked")
        T[] ts = (T[]) o;
        return ts;
    }
}

Output

[one, two, three]




Creating multidimensional arrays

package com.logicbig.example.array;

import java.lang.reflect.Array;
import java.util.Arrays;

public class NewInstanceExample3 {

    public static void main(String... args) {
        int d1 = 2;
        int d2 = 3;
        Object mainArray = Array.newInstance(int.class, d1, d2);
        for (int i = 0; i < d1; i++) {
            Object childArray = Array.newInstance(int.class, d2);
            Array.set(mainArray, i, childArray);
            for (int j = 0; j < d2; j++) {
                Array.set(childArray, j, i + j);
            }
        }

        String s1 = Arrays.deepToString((Object[]) mainArray);
        System.out.println(s1);
    }
}

Output

[[0, 1, 2], [1, 2, 3]]

See Also