Java by API/java.lang.reflect/Array

Array: clone()

  
/*
 Output:
Original size: 5
New size: 5
Original size: 9
New size: 9

 * */
public class MainClass {
  public static void main (String args[]) {
    int array1[] = {1, 2, 3, 4, 5};
    int array2[] = {1, 2, 3, 4, 5, 6, 7, 8, 9};
    System.out.println("Original size: " + array1.length);
    System.out.println("New size: " + cloneArray(array1).length);
    System.out.println("Original size: " + array2.length);
    System.out.println("New size: " + cloneArray(array2).length);
  }
  static int[] cloneArray(int original[]) {
    return (int[])original.clone();
  }
}

Array: getInt(Object array, int index)

  
/*
 Output:
Position: 0, value: 1040988893
Position: 1, value: -2073064706
Position: 2, value: -808861084
 * */
import java.lang.reflect.Array;
import java.util.Random;
public class MainClass {
  public static void main (String args[]) {
    Object array = Array.newInstance(int.class, 3);
    
    
    int length = Array.getLength(array);
    Random generator = new Random(System.currentTimeMillis());
    for (int i=0; i<length; i++) {
      int random = generator.nextInt();
      Array.setInt(array, i, random);
    }
    
    for (int i=0; i<length; i++) {
      int value = Array.getInt(array, i);
      System.out.println("Position: " + i + ", value: " + value);
    }
  }
}

Array: getLength(Object array)

  
/*
 Output:
Array of: int
Array size: 3
 * */
import java.lang.reflect.Array;
public class MainClass {
  public static void main (String args[]) {
    Object array = Array.newInstance(int.class, 3);
    
    Class type = array.getClass();
    if (type.isArray()) {
      Class elementType = type.getComponentType();
      System.out.println("Array of: " + elementType);
      System.out.println("Array size: " + Array.getLength(array));
    }
    
  }
}

Array: get(Object array, int index)

  
import java.lang.reflect.Array;
public class Main {
  public static Object copyArray(final Object input) {
    final Class type = input.getClass();
    if (!type.isArray()) {
      throw new IllegalArgumentException();
    }
    final int length = Array.getLength(input);
    final Class componentType = type.getComponentType();
    final Object result = Array.newInstance(componentType, length);
    for (int idx = 0; idx < length; idx++) {
      Array.set(result, idx, Array.get(input, idx));
    }
    return result;
  }
  public static void main(final String[] args) {
    try {
      int[] x = new int[] { 2, 3, 8, 7, 5 };
      char[] y = new char[] { "a", "z", "e" };
      String[] z = new String[] { "Jim", "John", "Joe" };
      System.out.println(" -- z and copy of z --");
      outputArrays(z, copyArray(z));
    } catch (final Exception ex) {
      ex.printStackTrace();
    }
  }

  public static void outputArrays(final Object first, final Object second) {
    if (!first.getClass().isArray()) {
      throw new IllegalArgumentException("first is not an array.");
    }
    if (!second.getClass().isArray()) {
      throw new IllegalArgumentException("second is not an array.");
    }
    final int lengthFirst = Array.getLength(first);
    final int lengthSecond = Array.getLength(second);
    final int length = Math.max(lengthFirst, lengthSecond);
    for (int idx = 0; idx < length; idx++) {
      System.out.print("[" + idx + "]\t");
      if (idx < lengthFirst) {
        System.out.print(Array.get(first, idx) + "\t\t");
      } else {
        System.out.print("\t\t");
      }
      if (idx < lengthSecond) {
        System.out.print(Array.get(second, idx) + "\t");
      }
      System.out.println();
    }
  }
}

Array: newInstance(Class<?> componentType, int... dimensions)

 

import java.lang.reflect.Array;
public class Main {
  public static void main(String[] argv) throws Exception {
    int[][] ints2 = (int[][]) Array.newInstance(int.class, new int[] { 10, 20 });
  }
}

Array: newInstance(Class componentType, int length)

  
/*
 Output:
Array of: int
Array size: 3
 * */
import java.lang.reflect.Array;
public class MainClass {
  public static void main (String args[]) {
    Object array = Array.newInstance(int.class, 3);
    
    Class type = array.getClass();
    if (type.isArray()) {
      Class elementType = type.getComponentType();
      System.out.println("Array of: " + elementType);
      System.out.println("Array size: " + Array.getLength(array));
    }
    
  }
}

Array: setInt(Object array, int index, int i)

  
/*
 Output:
Position: 0, value: 1040988893
Position: 1, value: -2073064706
Position: 2, value: -808861084
 * */
import java.lang.reflect.Array;
import java.util.Random;
public class MainClass {
  public static void main (String args[]) {
    Object array = Array.newInstance(int.class, 3);
    
    
    int length = Array.getLength(array);
    Random generator = new Random(System.currentTimeMillis());
    for (int i=0; i<length; i++) {
      int random = generator.nextInt();
      Array.setInt(array, i, random);
    }
    
    for (int i=0; i<length; i++) {
      int value = Array.getInt(array, i);
      System.out.println("Position: " + i + ", value: " + value);
    }
  }
}

Array: setLong(Object array, int index, long l)

  
import java.lang.reflect.Array;
public class Main {
  public static void main(String... args) {
    Object o = new int[2];
    Array.setShort(o, 0, (short) 2); // widening, succeeds
    Array.setLong(o, 1, 2L); // narrowing, fails
  }
}

Array: set(Object array, int index, Object value)

 
import java.lang.reflect.Array;
public class Main {
  public static void main(String[] argv) throws Exception {
    int[] array = { 1, 2, 3 };
    // Get the value of the third element.
    Object o = Array.get(array, 2);
    // Set the value of the third element.
    Array.set(array, 2, 1);
  }
}

Array: setShort(Object array, int index, short s)

  
import java.lang.reflect.Array;
public class Main {
  public static void main(String... args) {
    Object o = new int[2];
    Array.setShort(o, 0, (short) 2); // widening, succeeds
    Array.setLong(o, 1, 2L); // narrowing, fails
  }
}