This checker aims to improve the readability of new-style arrow switches by simplifying and refactoring them.

Simplifications:

• When a case consists only of a yielding some value, it can be re-written with just the value. For example, case FOO -> { yield "bar"; } can be shortened to case FOO -> "bar";
• When a case has redundant braces around the right-hand side of the arrow, they can be removed. For example, case FOO -> { System.out.println("bar"); } can shortened to case FOO -> System.out.println("bar");

Factoring out return switch:

• When every value of an enum is covered by a case which returns, the return can be factored out

enum SideOfCoin {OBVERSE, REVERSE};

private String renderName(SideOfCoin sideOfCoin) {
  switch(sideOfCoin) {
    case OBVERSE -> {
      return "Heads";
    }
    case REVERSE -> {
      return "Tails";
    }
  }
  // This should never happen, but removing this will cause a compile-time error
  throw new RuntimeException("Unknown side of coin");
}

The transformed code is simpler and elides the “should never happen” handler.

enum SideOfCoin {OBVERSE, REVERSE};

private String renderName(SideOfCoin sideOfCoin) {
  return switch(sideOfCoin) {
    case OBVERSE -> "Heads";
    case REVERSE -> "Tails";
  };
}

• When switching on something other than an enum, if the cases are exhaustive, then a similar refactoring can be performed.

Factoring out assignment switch:

• When every case just assigns a value to the same variable, the assignment can potentially be factored out
• If a local variable is defined and then immediately overwritten by a switch, the definition and assignment can potentially be combined

enum Suit {HEARTS, CLUBS, SPADES, DIAMONDS};

private void updateScore(Suit suit) {
  int score = 0;
  switch(suit) {
    case HEARTS, DIAMONDS -> {
      score = -1;
    }
    case SPADES -> {
      score = 2;
    }
    case CLUBS -> {
      score = 3;
    }
  }
}

Which can be consolidated:

enum Suit {HEARTS, CLUBS, SPADES, DIAMONDS};

private void updateScore(Suit suit) {
   int score = switch(suit) {
       case HEARTS, DIAMONDS -> -1;
       case SPADES -> 2;
       case CLUBS -> 3;
    };
}