Maximize font size while keeping text within JTextField

Question

I have a JTextField which may vary in size depending on resolution. The JTextField will hold a 3 letter string.

I want to set the font size of the JTextField in such a way to MAXIMIZE the font size while still having the text FIT inside of the JTextField perfectly.

Is there an algorithm to do this?

Answer 1

I have used Martijn's answer, along with the following answers:

String length in pixels in Java

Java: Getting a font with a specific height in pixels

...in order to write a full answer to my question. Here it goes. Thanks to all who contributed.

You will need to import the following:

import javax.swing.JTextField;
import java.awt.Font;
import java.awt.image.BufferedImage;
import java.awt.FontMetrics;
import java.lang.Math;

.................................

public int getFontSize(JTextField text, int columnsToHold){
            //Create a sample test String (we will it later in our calculations)
            String testString = "";
            for(int i = 0; i<columnsToHold; i++){
                  testString = testString + "5";
            }


             //size will hold the optimal Vertical point size for the font
      Boolean up = null;
      int size = text.getHeight();  
      Font font;
     while (true) {
        font = new Font("Default", 0, size);
        int testHeight = getFontMetrics(font).getHeight();
        if (testHeight < height && up != Boolean.FALSE) {
            size++;
            up = Boolean.TRUE;
        } else if (testHeight > height && up != Boolean.TRUE) {
            size--;
            up = Boolean.FALSE;
        } else {
           break;
        }
    }
        //At this point, size holds the optimal Vertical font size

        //Now we will calculate the width of the sample string
    BufferedImage img = new BufferedImage(1, 1, BufferedImage.TYPE_INT_ARGB);
    FontMetrics fm = img.getGraphics().getFontMetrics(font);
    int width = fm.stringWidth(testString);

        //Using Martijn's answer, we calculate the optimal Horizontal font size
    int newFontSize = size * textos[0].getWidth()/width;

        //The perfect font size will be the minimum between both optimal font sizes.
        //I have subtracted 2 from each font so that it is not too tight to the edges
    return Math.min(newFontSize-2, size-2);
}