whats is happening in this apex code? - salesforce

Question

String color1 = moreColors.get(0);
String color2 = moreColors[0];
System.assertEquals(color1, color2);
// Iterate over a list to read elements
for(Integer i=0;i<colors.size();i++) {
// Write value to the debug log
System.debug(colors[i]);
}
I am learning Apex and just started what is meaning of line System.assertEquals(color1, color2); and what is mean by debug log here?

Answer 1

System.assert, System.assertEquals, System.assertNotEquals. I argue these are three of the most important method calls in Apex.
These are assert statements. They are used in testing to validate that the data you have matches your expectations.
System.assert tests an logical statement. If the statement evaluates to True, the code keeps running. If the statement evaluates to False, the code throws an exception.
System.assertEquals tests that two values are equal. If the two are equal, the code keeps running. If they are not equal, the code throws an exception.
System.assertNotEqual tests that two values are not equal. If the two are not equal, the code keeps running. If they are equal, the code throws an exception.
These are critical for completing system testing. In Apex Code, you must have 75% line test coverage. Many people do this by generating test code that simply covers 75% of their lines of code. However, this is an incomplete test. A good test class actually tests that the code does what you expect. This is really great to ensure that your code actually works. This makes debugging and regression testing far easier. For example. Lets create a method called square(Integer i) that squares the integer returned.
public static Integer square( Integer i ) {
return i * i;
}
A poor test method would simply be:
#isTest
public static void test_squar() {
square( 1 );
}
A good test method could be:
#isTest
public static void test_square() {
Integer i;
Integer ret_square;
i = 3;
ret_square = square( i );
System.assertEquals( i * i; ret_square );
}
How I would probably write it is like this:
#isTest
public static void test_square() {
for( Integer i = 0; i < MAX_TEST_RUNS; i++ ) {
System.assertEquals( i*i, square( i ) );
}
}
Good testing practices are integral to being a good developer. Look up more on Testing-Driven Development. https://en.wikipedia.org/wiki/Test-driven_development

Answer 2

Line by Line ...
//Get color in position 0 of moreColors list using the list get method store in string color1
String color1 = moreColors.get(0);
//Get color in position 0 of moreColors list using array notation store in string color2,
//basically getting the same value in a different way
String color2 = moreColors[0];
//Assert that the values are the same, throws exception if false
System.assertEquals(color1, color2);
// Iterate over a list to read elements
for(Integer i=0;i<colors.size();i++) {
// Write value to the debug log
System.debug(colors[i]);//Writes the value of color list ith position to the debug log
}
If you are running this code anonymously via the Developer console you can look for lines prefixed with DEBUG| to find the statements, for e.g.
16:09:32:001 USER_DEBUG 1|DEBUG| blue
More about system methods can be found at https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_methods_system_system.htm#apex_System_System_methods