Output formatting

It's very disturbing. We will learn just few common ones.

Introduction

As the name suggest, it is for formatting the output before showing to user. Let's learn some:

printf style formatting

• It is similar to printf style formatting.

• Integer formatting:

  • General syntax

    %<argument_index$><flags><width><conversion>
    

  • Representation type:
    • d = for base 10 (decimal)
    • o = for base 8 (octal)
      • if # used at first, then output begins with 0.
    • x = for base 16 (hexadecimal)
      • • if # used at first, then output begins with 0x.
  • '' is just for showing space:

    int num = 1234;
    int num2 = 21;
    System.out.printf("%1$2d\n", num); // '1234'
    System.out.printf("%1$6d %2$d\n", num, num2); // '  1234 21'
    

  • Here, for %1$6d:
    • %1: 1 means the first argument,
    • $6: 6 space will be taken total.
      • positive: extra space will be added on left,
      • negative: extra space will be added on right.
    • d: means integer.
  • More examples:

    final int num = 2007224;
    
    System.out.printf("%d\n", num); // 2007224
    
    // Number with single quotes
    System.out.printf("'%d'\n", num); // '2007224'
    
    // Extra space on left
    System.out.printf("%10d\n", num); //   2007224
    
    // Extra space on right
    System.out.printf("%-10d\n", num); // 2007224   //
    
    System.out.printf("%010d\n", num); // 0002007224
    
    // Enclose negative number in parentheses
    System.out.printf("%(d\n", num); // 2007224
    System.out.printf("%(d\n", -num); // (2007224)
    
    // Number with sign
    System.out.printf("%+d\n", num); // +2007224
    System.out.printf("%+d\n", -num); // -2007224
    

• Floating point number:

  • For floating point data type float, double, BigDecimal.
  • Representation type:
    • e = for locale specific computerized scientific notation
    • f = for locale specific decimal format
    • g = locale specific general scientific notation
      • Acts as e if value < 10^-4 or precision >= 10
      • Acts as f if value > 10^-4 or precision < 10
  • Example:

    System.out.printf("%f\n", 10.2); // 10.200000
    
    // 3 digits after decimal point
    System.out.printf("%.3f\n", 10.2); // 10.200
    System.out.printf("%e\n", 10.2); // 1.020000e+01
    
    // Act as e
    System.out.printf("%g\n", 0.000002079); // 2.07900e-06
    // Act as f
    System.out.printf("%g\n", 0.207); // 0.207000
    
    System.out.printf("%f\n", 0.000002079); // 0.000002
    

• Character formatting

  • For data type char, Character, and if in valid range then byte, short, int.
  • Representation type: c
  • Example:

    char ch = 'b';
    // Normal printing
    System.out.printf("%c\n",ch); // b
    System.out.printf("%C\n",ch); // B
    
    // using ASCII value
    System.out.printf("%c\n",97); // a
    
    // Extra space at left
    System.out.printf("%5c\n",'a'); //     a
    
    // Extra space at right
    System.out.printf("%-5c\n",'a'); // 'a    '
    

Date time formatting will be discussed later