OCP 17 Exam - chapter 1 notes

Chapter 1 notes:

• source file must have at most one public type
• import that specifies class name takes precedence over import with * if there are two classes with the same name
  • e.g. java.util.Date vs. java.sql.*, which also provides Date class
• types - boolean size is not specified, depends on JVM

  • byte

    8 bit

    -128

    127

  • short

    16 bit

    -32,768

    32,767

  • int

    32 bit

    -2,147,483,648

    2,147,483,647

  • long

    64 bit

    -2^63

    2^63 - 1

  • float

    32 bit

    n/a

  • double

    64 bit

    n/a

  • char

    16 bit

    0

    65,535

• string text block - if you put ending """ in new line, it will result in blank line
  • \ - joins lines - line break is ignored
  • \s - add extra twi spaces at the end of line
• underscore in number literals can be used only inside, we cannot start or end number with _ or use near .
  • correct: 1___1_1.1___1_1
• variable name must start with letter, _, or currency symbol like $, €, ¥
• declaration of multiple variables in the same line is only possible for the same type, except var!
  • e.g. int v1 = 1, v2, v3 = 3;
• you can declare array in two ways: int[] arrayName or int arrayName[]
• var var = "var" is allowed because var is not reserved word, just reserved type!
• curly braces can be used inside class or method and they define new scope
  • when used in class it is called
• “identifying blocks and variable scope is second nature of the exam” ;)
• object vs. references - “all references are the same size, but object can have different size”

Fundamentals exam notes from practise attempt:

• cast: if we assign smaller type size to larger, e.g. int to long or byte to short then we don’t need cast.
  • short to char and vice-versa also needs a cast
• “functional interface must have exactly one abstract method and may have other default or static methods”
• “break w/o a label can occur only in a switch, while, do, or for statement”
• “interfaces allow multiple implementation inheritance through default methods” - Java doesn’t allow to extend from multiple classes
• trim is method of String, not StringBuilder