How can you write single line comments in Java?

What is the output produced by the following lines of program code?

char x, y;
x = 'y';
System.out.println(x);
y = 'z';
System.out.println(y);
x = y;
System.out.println(x);

What are symbolic constants? How are they useful in writing programs?

Write a Java constant declaration that gives the name TAX_RATE to the value 15%.