OCP 17 Exam - chapter 3 notes (switch, loops, pattern matching, flow scoping)

• “watch indentation and braces”, e.g. in the following example count is always incremented

if (count < 2)
	System.out.println("Good day");
    count++;

• “pattern matching was introduced to reduce boilerplate code, … like a lot of other new enhancements in Java”
• reassigning pattern variables is possible (can be prevented with final)

if (count instanceof final Integer i)
    i = 5; // DOES NOT COMPILE

• pattern variable must be subtype

Double d = 2.0;
if(d instance of Double)
if(d instance of Double data) // DOES NOT COMPILE, but compiles in JAVA 21

• flow scoping - “scope is determined by compiler, not hierarchy like class or local scoping”

private static flowScopingShowcase(Number num) {
    if(!(number instance Integer integer))
        return
    System.out.println("it's integer " + integer.intValue());
}

• switch statement
  • case constantExpresion: { System.out.print("value"); }
  • break is optional. When case is matched and there will be no break;, then all subsequent cases will be evaluated as well.
  • default can be placed anywhere - doesn’t have to be at the end
  • we can combine case in two ways: case 1: case 2: or case 1,2: (since Java 14)
  • supported types: int, byte, short, char, String, enum and var (if resolved to mentioned types)
  • if case statement is defined locally, then must be final -
• switch expressions
  • case constantExpresion -> { yield "value"; }
  • assignment to variable is optional
  • default is only required if assigned to variable and not all cases were covered
  • if assigned to variable it must end with ;
  • block with } cannot end with ; (for switch statement it can!)
• loops
  • we can use var in for-each loop: for(var name : names)
  • statements after break; DOES NOT COMPILE
  • break LABEL; will go to expression stating with LABEL:
  • tip on exam is to SKIP too complex loops, because I won’t get extra points for solving this!

Playground code

https://github.com/RG9/rg-playground-ocp17/blob/main/Chapter3.java

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Credit: OCP Oracle Certified Professional Java SE 17 Developer Study Guide