It is not a Netbeans or Java theme. You can check on Wikipedia that:
The ASCII code reserves the first 32 codes (numbered from 0 to 31)
in decimal) for control characters: unintended codes
originally to represent printable information, but to
Control devices (such as printers) that used ASCII. By
example, character 10 represents the "new line" function (line
feed), which makes a printer advance the paper, and the character 27
represents the "escape" key that is often found in the corner
top left of common keyboards.
And 32 does show it to you, what happens is that it is space.
33 is the first visible (considering space as "not visible") and is the exclamation point
Actually, as you can check with the characters of your question, if you have the font (font) compatible, those characters are displayed, but in a console or system terminal they are not usually shown:
But even to show it here, the browser uses other codes: the heart is the code 9829 (2665 in hexadecimal):