New to Java

I find myself needing to be able to produce a list of all possible combinations of letters (case-insensitive) between 1 and 20 characters. A perfect job for a computer to do. Unfortunately, I'm a moron, and can't quite figure out how to code this. Using my current method, I'd have thousands of for loops and very sore fingers. Can someone help me out and show me a better way to do this?

Desired output format:

a
b
c
a,a
b,a
c,a
a,b
b,b
c,b
a,c
b,c
c,c
a,a,a
b,a,a
c,a,a
a,a,b
b,a,b
c,a,b
a,a,c
b,a,c
c,a,c
a,b,a
b,b,a
c,b,a
a,b,b
b,b,b
c,b,b
a,b,c
b,b,c
c,b,c
a,c,a
b,c,a
c,c,a
a,c,b
b,c,b
c,c,b
a,c,c
b,c,c
c,c,c

The ugly code I used to create the above list:

var arr = new Array();
var alphabet = new Array("a","b", "c");
for(var x=0;x<3;x++){ 
arr[0]=alphabet[x];
document.write('<br>' + arr);
}

for(var y=0;y<3;y++){
arr[0]=alphabet[y];
arr[1]=alphabet[0];
document.write('<br>' + arr);
}
for(var y=0;y<3;y++){
arr[0]=alphabet[y];
arr[1]=alphabet[1];
document.write('<br>' + arr);
}
for(var y=0;y<3;y++){
arr[0]=alphabet[y];
arr[1]=alphabet[2];
document.write('<br>' + arr);
}
for(var y=0;y<3;y++){
arr[0]=alphabet[y];
arr[1]=alphabet[0];
arr[2]=alphabet[0];
document.write('<br>' + arr);
}
for(var y=0;y<3;y++){
arr[0]=alphabet[y];
arr[1]=alphabet[0];
arr[2]=alphabet[1];
document.write('<br>' + arr);
}
for(var y=0;y<3;y++){
arr[0]=alphabet[y];
arr[1]=alphabet[0];
arr[2]=alphabet[2];
document.write('<br>' + arr);
}
for(var y=0;y<3;y++){
arr[0]=alphabet[y];
arr[1]=alphabet[1];
arr[2]=alphabet[0];
document.write('<br>' + arr);
}
for(var y=0;y<3;y++){
arr[0]=alphabet[y];
arr[1]=alphabet[1];
arr[2]=alphabet[1];
document.write('<br>' + arr);
}
for(var y=0;y<3;y++){
arr[0]=alphabet[y];
arr[1]=alphabet[1];
arr[2]=alphabet[2];
document.write('<br>' + arr);
}
for(var y=0;y<3;y++){
arr[0]=alphabet[y];
arr[1]=alphabet[2];
arr[2]=alphabet[0];
document.write('<br>' + arr);
}
for(var y=0;y<3;y++){
arr[0]=alphabet[y];
arr[1]=alphabet[2];
arr[2]=alphabet[1];
document.write('<br>' + arr);
}
for(var y=0;y<3;y++){
arr[0]=alphabet[y];
arr[1]=alphabet[2];
arr[2]=alphabet[2];
document.write('<br>' + arr);
}