// Comma used to separate a list of variable declarations
int a=20, b=30, c=80;

// Comma used to separate a list of values assigned to an array
int[] d = { 20, 60, 80 };

// Comma used to separate a list of parameters passed to a function
line(a, b, c, b);
line(d[0], d[1], d[2], d[1]);