How to increase String input for every time component method is called

I just started learning coding (mainly Java) for about 6 months at a University and now we just covered section of Composite design pattern (with Component, Leaf and Composite classes).

My class problem requires I use the below Component Interface to make a simple director program that I can create/add/remove files/directory.

public interface Component {
    public String getName();
    public int getSize();
    public int getCount();
    public String display(String prefix);
    public Component search(String name);
}

Below is the File class that I wrote to be used as Leaf

public class File implements Component { 
    private String name;
    private int size;
    public File(String name, int size){
        this.name = name;
        this.size = size;
    }
    
    @Override
    public String getName() {
        return this.name;
    }
    
    @Override
    public int getSize() {
        return this.size;
    }
    
    @Override
    public int getCount() {
        return 1;
    }
    
    @Override
    public String display(String prefix) {
        return this.name + " " + "(" + this.size + ")" + System.lineSeparator();
    }
    
    @Override
    public Component search(String name) {
        if(this.name.equals(name)){
            return this;
        }
        else {
            return null;
        }
    }

Below is the Component Class - Directory Class. I put line of * above the method display in question.

import java.util.ArrayList;

public class Directory implements Component {
    static int count = 0;
    private String name;
    //Array List to store the leafs
    public ArrayList<Component> children;

    public Directory(String name){
        this.name = name;
        this.children = new ArrayList<>();
    }

    //Method to add leaf to Directory
    public void add(Component component){
        children.add(component);
    }

    //Method to remove leaf from Directory
    public void remove(Component component){
        children.remove(component);
    }

    @Override
    public String getName() {
        return this.name;
    }

    @Override
    public int getSize() {
        int size = 0;
        for(Component component : children) {
            size += component.getSize();
        }
        return size;
    }

    @Override
    public int getCount() {
        int count = 0;
        for(Component component : children) {
            count += component.getCount();
        }
        return count;
    }

//***********************************
    @Override
    public String display(String prefix) {
        String totalString = name + ": (count=" + getCount() + ", size=" + getSize() + ")" + System.lineSeparator();

        for (Component component : children) {
            totalString = totalString + prefix + component.display(prefix + prefix);
        }
        return totalString;
    }

//*************************************
    @Override
    public Component search(String name) {
        for(Component component: children) {
            if (component.search(name) != null) {
                return component;
            }
        }
        return null;
    }
}

My goal is, when I apply the display method, every-time the component has children, the prefix in display method should increase by 1. To clarify, below is my test method

public class Test3 {

    public static void main(String[] args) {
        File holiday = new File("family-holiday",201);
        File wallpaper = new File("wallpaper", 421);
        Directory pictures = new Directory("pictures");
        Directory personal = new Directory("personal");
        Directory misc = new Directory("misc");
        Directory dog = new Directory("dog");
        dog.add(wallpaper);
        personal.add(holiday);
        personal.add(misc);
        pictures.add(personal);
        misc.add(dog);

        System.out.print(pictures.display("+"));
    }
}

The result of this should be

pictures: (count=2, size=622)
\+personal: (count=2, size=622)
\++family-holiday (201)
\++misc: (count=1, size=421)
\+++dog: (count=1, size=421)
\++++wallpaper (421)

However, due to the display method when component has children, it calls (prefix + prefix) which works until the 3rd directory/files, the prefix gets doubled every time instead of an increment of one. Below is the result I got

pictures: (count=2, size=622)
\+personal: (count=2, size=622)
\++family-holiday (201)
\++misc: (count=1, size=421)
\++++dog: (count=1, size=421)
\++++++++wallpaper (421)

I have tried multiple ways that I can think of below

• Add prefix at the File display : This obviously did not work if there is director inside directory

• Use static parameter to count number of method getting called, since the number of times prefix should be used depends on how many level the file / director is in there, that doesn't work with full count of the number of times used by the method.

• Adding prefix at MANY MANY different places .. :) Still did not work well. I can imagine it has to be the way I pass the prefix to when the loop is calling display again, but I can't figure out what it is ...

If you could please advise or guide on what I can do or what I should read on to help with this, that will be very helpful. I do apologise in advance if there is similar topics as I couldn't find them with my current knowledge of the keyword, if you could please guide me there then I'm very grateful

As I said, just pass the depth as an integer and construct the prefix within the display function.

    @Override
    public String display(int depth) {
        String prefix = '+'.repeat(depth);
        String totalString = name + ": (count=" + getCount() + ", size=" + getSize() + ")" + System.lineSeparator();

        for (Component component : children) {
            totalString = totalString + prefix + component.display(depth + 1);
        }
        return totalString;
    }

...

        System.out.print(pictures.display(1));