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Arrays 

 
/**
 * One way to create an array is with new operator ...
 * which allocates the memory for 3 elements
 * 
 * You can also create and initialize the array with {} syntax
 * Array length is the number of elements between braches
 */

package com.minte9.basics.arrays;

public class Arrays {
    public static void main(String[] args) {
        
        int[] nums; 
        nums = new int[2]; 
        nums[0] = 1;
        nums[1] = 2;
        
        String[] names = {"John", "Marry", "Ana"};

        System.out.println(nums[1]);  // 2
        System.out.println(names[2]); // Ana

        try {
            names[3] = "Willy";
        } catch (Exception ex) {
            System.out.println(ex.getMessage()); // Index 3 out of bounds
        }
    }
}

Types 

 
/**
 * An array is forever an array
 * 
 * Creating an array of Dogs, not a new Dob object
 */
package com.minte9.basics.arrays;

public class Types {
    public static void main(String[] args) {
    
        Dog[] dogs = new Dog[4]; // array of Dogs
        dogs[0] = new Dog();
        dogs[1] = new Dog();
     // dogs[2] = 222; // Compiler Error 
        
        System.out.println(dogs.length); // 4
    }
}

class Dog {}

Join 

 
/**
 * Array string elements can be joined with ...
 * String.join() method (since JDK 1.8)
 */

package com.minte9.basics.arrays;

public class Join {
    public static void main(String[] args) {
        
        String[] A = new String[] {"a", "b", "c"};
        System.out.println(

            String.join(", ", A) // a, b, c
        );  
    }
}






Questions and answers:
Clink on Option to Answer




1. What does using the new operator do when creating an array?

  • a) Allocates memory for a fixed number of elements
  • b) Automatically fills the array with values

2. What determines the length of an array created with {} syntax?

  • a) The highest index used
  • b) The number of elements inside the braces

3. What happens if you access an array index that is out of bounds?

  • a) A runtime exception is thrown
  • b) The value is set to null

4. Once created, what can an array store?

  • a) Any type of value
  • b) Only elements of its declared type

5. How can string elements of an array be combined into one string?

  • a) Using String.join()
  • b) Using Arrays.toString() only

6. Why is an array described as “forever an array”?

  • a) Because it cannot be resized
  • b) Because its type cannot change


References: