How to make a drag and drop component in java?

so i'm writing a program and it requires 4 little circles to be dragged and dropped onto certain positions. its all inside a JFrame. i want there to be 4 specific spots where the circles start out. then as you drag them a small line from where the circle started to the the circle no matter where i move it. i also want it so that when i release the circle in an area where i don't want it it will be pulled back to the original position. ALso i need a way to check the position of the circle and set it to a variable.this is probably EXTREMELY complicated. Ive been combing the internet for days and jut cant figure it out. thanks in advance!