Thread: How to think about LOOPS in the first place

Recommended reading: The for Statement (The Java™ Tutorials > Learning the Java Language > Language Basics)

I'm not sure exactly what you're confused about. Could you provide an example SSCCE that demonstrates something that you're not clear on?

Thanks for your reply and sorry, if I posted my thread on the wrong sub-forum. This is an example of a problem that I could not figure out how to construct loops to solve it.

Write an application that displays the following patterns separately, one below the other. Use for loops to generate the patterns. All asterisks should be printed by a single statement of the form System.out.print( '*' ); which causes the asterisks to print side by side. A statement of the form System.out.println(); can be used to move to the next line. A statement of the form System. out.print( ' ' ); can be used to display a space for the last two patterns. There should be no other output statements in the program.

Modify the previous exercise to combine your code from the four separate triangles of asterisks
such that all four patterns print side by side

image.jpg

This intuition comes with practice. As you program more, you'll figure out where are good places to use loops and how to use them effectively. Also, loops are a lot about math (particularly for loops).

One way to help you think about assignments like this is by using a piece of paper and a pencil. Draw this out by hand, labeling stars and spaces with numbers. Do you see a pattern?

Hint: you can put loops inside of loops.

Okay let's take a real problem: You want to write a file listing function. This means you have to recursively run through all directories and subdirectories.
The first question you ask yourself is: What do I need? -> Files. Next: How do I interact with files? -> File Class

Take this small piece of code

public class Listing{
   //fields
  private File file; //You declared a File with name file
 
  //constructor
  public Listing(){
     this.file = new File("C:/text.txt");
   }
 
  public String toString(){
   System.out.println(this.file.getName());
   }
}

Now you got one file you can talk to. So say we want to get all the files in a directory now:

public class Listing{
   //fields
  private File file; //You declared a File with name file
  private File folder; //A folder is also a file
  //constructor
  public Listing(){
     this.folder = new File("C:/test);
   }
 
  public void getFiles(){
    if(folder.isDirectory()){
      File[] files = folder.listFiles(); //put all the files in an array
      //Now what you have to do is iterate through the list till you reach the end.
     /* Important to note is that arrays, collections, etc. all have one thing in common... 
         They have a size. It's important to know the size, because this will be the max of your loop (for now)
     */
      //You can use whatever kind of loop you which, I'm going to use a for loop because it's the shortest
                 for(int i=0; i<files.length(); i++){
                   //important to note is that arrays have lengths, but if I were to work with a collection it would be a size.
                      System.out.println(files[i].getName());  
                 }
      //Such a loop is still too consuming, that's why most people use a for-each loop when iterating through lists to show their contents. NEVER USE A FOR EACH LOOP      TO CHANGE THE VALUE OF AN OBJECT... It's just not good programming manners
               for(File f:files){
                    System.out.println(f.getName());  //As you can see much less code
               }
        }
   } 
 
  public String toString(){
   System.out.println(this.file.getName());
   }
}

Now this is a basic concept: When you want to create loops you have to think: What do I want to loop through? Objects? Numbers? Do I want to stop at a certain point? (If statement in your loop) Do I want to read or write/alter data? (for-each or for/while/do while)

Note: this is pseudo code, it might give an error or two I don't know, I just came up with it on the spot
I'm sparing real recursion because it's somewhat more advanced, but this is the basic one folder search