MSC13-J. Finish every set of statements associated with a case label with a break statement

A switch statement is comprised of several case labels, and a default label. The default label is not required, but strongly recommended. The statements following a case label conventionally end with a break; statement, which moves control flow to the end of the switch block. If omitted, control flow falls through to the next case statement in the switch block. Because the break statement is not required, omitting it produces no compiler warnings, and if this was unintentional, it can lead to an unexpected control flow.

Noncompliant Code Example

In this noncompliant code example, the case where card = 11 does not have a break statement. Thus, the statements for card = 12 are also executed when card = 11.

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

In the compliant solution, each case label is ended 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

EX1: The last label in a switch statement requires no break. The break statement serves to skip to the end of the switch block, so control flow will continue to statements following the switch block with or without it. . Conventionally, the last label is the default label.
EX2: In some cases, where control flow is intended to execute the same code for multiple cases, it is permissible to omit the break statement. However, these instances must be explicitly documented.

int card=11;
int value;

/* Case 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 */ 
}

EX3: A case block needs no break statement if its last statement is return or throw.

Risk Assessment

Failure to include break statements leads to unexpected control flow.

Other Languages

This rule appears in the C Secure Coding Standard as MSC17-C. Finish every set of statements associated with a case label with a break statement.

This rule appears in the C++ Secure Coding Standard as MSC18-CPP. Finish every set of statements associated with a case label with a break statement.

References

[[JLS 05]] Section 14.11 The switch Statement