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Java Literals

When we write a numeric literal in our code, Java interprets it as base-10 or decimal.

  • If we code int i = 12, that's 12; a dozen.

Non-decimal Literals

A leading zero in front of a number doesn't change its magnitude.

  • It does change how Java interprets the number.

Octal

A simple leading 0 tells Java our number is base-8 or octal.

  • If we code int i = 012, it's octal 12 (1*8 + 2*1): actually a decimal 10.

Hexadecimal

When we add a leading 0x, we're telling Java our number is base-16 or hexadecimal.

  • If we code int i = 0x12, (1*16 + 2*1): that's actually a decimal 18.

  • If we code int i = 0xa, that's a decimal 10.

  • We could also code this as 0x000a.

Binary

When we add a leading 0b, we're telling Java our number is base-2 or binary.

  • If we code int i = 0b12 we get a compiler error: there's no 2 in binary.

  • If we code int i = 0b10, (1*2 + 0*1) that's actually a decimal 2.

  • We could also code this as 0b00000010 as a reminder there's eight bits in a byte.

Practice Exercise

For all of these Java numeric literals that contain alphabetic characters, it doesn't matter if you use lower or upper case: 

i = 0B0100;
i = 0X123AbC;
Reference: https://docs.oracle.com/javase/specs/jls/se8/html/jls-3.html#jls-3.10.1

Formatting

You can use underscores in all of these for readability.

int ipAddress = 0xc0_a8_01_65;
int permissions = 0b0_110_100_100;
char newLine = 012;  // ASCII 10, aka '\n'
int oneMillion = 0b00000000_00001111_01000010_01000000;
  • Remember the rule for _ in number literals: there must be a digit or another underscore on either side.
int i = 0x_1abc;        // NO
int k = 0b01001_;       // NO
float f = 0x01abc_.246; // NO

Drill

Yes or no: which of these declarations will compile? 

int i1 = 678;
int i2 = 0678;
int i3 = 0x678;
int i4 = 01101;
int i5 = 0b1101;
int i6 = 0x01101;
int i7 = 1101;
int i8 = 0x12;
int i9 = 0b12;
int ia = 0xb2;
int ib = 0bx2;
int ic = 0b_101_111_111;
int id = 0xb10_000;
int ie = 0b10_000;
int if_ = 0xCAFE_BABE;

double d1 = 123.456;
double d2 = 1.235_56;
double d43 = 123._456;

Solution: NumeralSystems/com.example.numeralsystems.solutions.SkillDrills2.java

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