A switch block comprises several case labels and an optional but highly recommended default label. Statements that follow each case label must end with a break statement, which is 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.
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;
}
|
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;
}
|
*MSC09-EX0*: 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 \[java:[Rogue 2000|AA. Bibliography#Rogue 00]\]). |
MSC09-EX1: When multiple cases require execution of identical code, then break statements may be omitted from all cases except the last one. 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: // break not required
case 12: // break not required
case 13:
value = 10;
break; // break required
default:
// Handle Error Condition
}
|
MSC09-EX2: When a case ends with a return or throw statement, the break statement may be omitted.
Failure to include break statements can cause unexpected control flow.
Rule |
Severity |
Likelihood |
Remediation Cost |
Priority |
Level |
|---|---|---|---|---|---|
MSC09-J |
medium |
unlikely |
low |
P6 |
L2 |
MSC17-C. Finish every set of statements associated with a case label with a break statement |
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MSC18-CPP. Finish every set of statements associated with a case label with a break statement |
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[ISO/IEC TR 24772:2010 |
http://www.aitcnet.org/isai/] |
"Switch Statements and Static Analysis [java:CLL]" |
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CWE-484, "Omitted Break Statement in Switch" |
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[java:[JLS 2005 |
AA. Bibliography#JLS 05]] |
[Section 14.11 The switch Statement |
http://java.sun.com/docs/books/jls/third_edition/html/statements.html#14.11] |
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[java:[Rogue 2000 |
AA. Bibliography#Rogue 00]] |
[The Elements of Java Style |
http://www.ambysoft.com/books/elementsJavaStyle.html], Rule 78. |
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49. Miscellaneous (MSC) MSC57-J. Use inequality operators to terminate loops whose counter changes by more than one