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The {{char}} type is the only unsigned primitive type in Java. As a result, a signed value cannot be stored and retrieved successfully from a variable of type {{char}}. In particular, comparing a value of type {{char}} with -1 will never yield {{true}}.  However, because the method {{read()}} returns -1 to indicate the End of File ({{EOF}}) condition, it is tempting to compare the character returned by {{read()}} with -1.  This is a common error \[[Pugh 08|AA. Java References#Pugh 08]\].

Noncompliant Code Example

In this This noncompliant code example , casts the value of type int returned by the read() method is cast directly to a value of type char which is compared with -1 to try to detect EOF. This conversion leaves the value of c as 0xffff (Character.MAX_VALUE) instead of -1. As a result, this test never evaluates to true.

char c;
while ((c = (char) in.read()) != -1) { 
  // ... 
}

Compliant Solution

Always use a signed type of sufficient size to store signed data. To be compliant, use a value of type int to check for EOF while reading in data. If the value of type int returned by read() is not -1, then it can be safely cast to a value of type char.

int c;
while ((c = in.read()) != -1) { 
  ch = (char) c; ... 
}

Risk Assessment

Storing signed data in a variable of the unsigned type char can lead to misinterpreted data and possibly memory leaks. Furthermore, comparing a value of type char with -1 never evaluates to true. This error could lead to can result in a denial-of-service attack.

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