PROGRAMMING

m9/ JAVA
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Last update:   18-10-2021

Arrays

Arrays can be created with new operator, or alternatively with {} syntax.
 
/**
 * One way to create an array si with new operator ...
 * which allocates the memory for 3 elements.
 * 
 * You can also create and initialize the array with {} syntax
 * Here the length of the array is the number of ...
 * elements between braches.
 */

package com.minte9.basics.arrays;

public class Arrays {
    public static void main(String[] args) {
        
        /**
         * create an array of integers and ..,
         * initialize the array with 3 integers
         */
        int[] nums; 
        nums = new int[3]; 
        nums[0] = 1;
        nums[1] = 2;
        nums[2] = 3;
        System.out.println(nums[2]); // 3

        /**
         * create and intialize an array with 3 strings
         */
        String[] names = {"John", "Marry", "Ana"};
        System.out.println(names[2]); // Ana

        /**
         * tring to assign a new value raises an ...
         * out of bonds error
         */
        names[3] = "Willy";
    }
}

... 26 lines
 

Types

p83 An array is forever an array.
 
/**
 * An array is forever an array.
 * 
 * In this app we are 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 
    }
}

class Dog {}

... 9 lines
 

Join

Starting with Java 8 we can use String.join() method.
 
/**
 * 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[] letters = new String[] {"a", "b", "c"};
        System.out.println(

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

... 6 lines
 

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