how to set value of octal in java?

I am trying to write following code.but it gives me error kindly help me.

    int six=06;
    int seven=07;
    int abc=018;
    int nine=011;
    System.out.println("Octal 011 ="+nine);
    System.out.println("octal O18 =" + abc);

why i cant give 018 and 019 to variable.i can give value 020 and 021 to variable. Why this happen? what's the reason behind this Kindly tell me.
I got Following error

            integer number too large: 018
            int eight=018;

Octal is base-8 number system, so it means digit can be from 0 to 7, you can't use digit 8 (and 9 too) in octal number system.

// Decimal declaration and possible chars are [0-9]
int decimal    =  495;        

// HexaDecimal declaration starts with 0X or 0x and possible chars are [0-9A-Fa-f]
int hexa       =  0X1EF; 

// Octal declaration starts with 0 and possible chars are [0-7] 
int octal      =  0757;  

// Binary representation starts with 0B or 0b and possible chars are [0-1]  
int binary     =  0b111101111; 

If the number is string format then you can convert it into int using the below

String text = "0b111101111";
int value = text.toLowerCase().startsWith("0b") ? Integer.parseInt(text.substring(2), 2)
                                  : Integer.decode(text);