MSC14-J. Finish every set of statements associated with a case label with a break statement

A switch block comprises several case labels and an optional but highly recommended default label. By convention, statements that follow each case label end with a break statement, responsible for transferring the control to the end of the switch block. When omitted, the statements in the subsequent case label are executed. Because the break statement is optional, omitting it produces no compiler warnings. When this behavior is unintentional, it can cause unexpected control flow.

Noncompliant Code Example

In this noncompliant code example, the case wherein the card is 11, lacks a break statement. As a result, execution continues with the statements for card = 12.

int card = 11;

switch (card) {
  /* ... */
  case 11: 
    System.out.println("Jack");
  case 12: 
    System.out.println("Queen"); 
    break;
  case 13: 
    System.out.println("King"); 
    break;
  default: 
    System.out.println("Invalid Card"); 
    break;
}

Compliant Solution

This compliant solution terminates each case (including the default case) with a break statement.

int card = 11;

switch (card) {
  /* ... */
  case 11: 
    System.out.println("Jack");
    break;
  case 12: 
    System.out.println("Queen"); 
    break;
  case 13: 
    System.out.println("King"); 
    break;
  default: 
    System.out.println("Invalid Card"); 
    break;
}

Exceptions

MSC14-EX1: The break statement at the end of the final case in a switch statement may be omitted; by convention, this is the default label. The break statement serves to transfer control to the end of the switch block; fall-through behavior also causes control to arrive at the end of the switch block. Consequently, control transfers to the statements following the switch block without regard to the presence or absence of the break statement. Nevertheless, the final case in a switch statement should end with a break statement, in accordance with good programming style (see [[Rogue 2000]]).

MSC14-EX2: A break statement may be omitted when multiple cases require execution of identical code. Such instances must be explicitly documented. For example:

int card = 11;
int value;

// Cases 11,12,13 fall through to the same case 
switch (card) {
  // MSC13-J:EX2: these three cases are treated identically 
  case 11: 
  case 12: 
  case 13: 
    value = 10; 
    break;
  default: 
    // Handle Error Condition 
}

MSC14-EX3: When a case ends with a return or throw statement, the break statement may be omitted.