Bad Practice
- CNT: Rough value of known constant found
- BC: Equals method should not assume anything about the type of its argument
- SW: Certain swing methods needs to be invoked in Swing thread
- BIT: Check for sign of bitwise operation
- CN: Class implements Cloneable but does not define or use clone method
- CN: clone method does not call super.clone()
- CN: Class defines clone() but doesn’t implement Cloneable
- Co: Abstract class defines covariant compareTo() method
CNT: Rough value of known constant found
Example
In this example the circumference of a circle is calculated. The value ̣π is is inserted as an approximate value. It is better to use a constant (e.g. Math.PI).
circumference = diameter * 3.141;
Restrictions
This bug is only found when a certain threshold is exceeded (see the not detected example).
Suppression
This warning can be suppressed with @SuppressFBWarnings(value="CNT_ROUGH_CONSTANT_VALUE").
Project examples
- Detected KnownConstant Line 27
- Not Detected KnownConstant Line 31
- Suppressed KnownConstant Line 34
NP: Method with Boolean return type returns explicit null
Example
In this example a method with the return type Boolean returns null directly. This will be found by spotbugs and marked as bug.
public Boolean booleanMethod() {
return null;
}
Restrictions
This bug will not be found when a variable is defined which can return null.
public Boolean variableBooleanMethod() {
Boolean result = null;
return result;
}
Suppression
This warning can be suppressed with @SuppressFBWarnings(value="NP_BOOLEAN_RETURN_NULL").
Project examples
- Detected BooleanReturnsNull Line 27
- Not Detected BooleanReturnsNull Line 32
- Suppressed BooleanReturnsNull Line 35
SW: Certain swing methods needs to be invoked in Swing thread
Example
In this example the method setVisible() is called from the main thread which can cause deadlocks or calling methods on partially created Swing components.
public static void main(String... args) {
JFrame jFrame = new JFrame();
jFrame.setVisible(true);
}
Restrictions
This bug is only found when the problematic code is called in the main thread (directly from the main() method).
Fixing
To fix the bug ensure that the problematic methods are called from the event dispatching thread.
SwingUtilities.invokeLater(new Runnable() {
@Override
public void run() {
jFrame.setVisible(true);
}
});
Suppression
This warning can be suppressed with @SuppressFBWarnings(value="SW_SWING_METHODS_INVOKED_IN_SWING_THREAD").
Project examples
- Detected BugSwingThread Line 30
- Not Detected BugSwingThread Line 35
- Fixed FixedSwingThread Line 31
- Suppressed SuppressSwingThread Line 28
BC: Equals method should not assume anything about the type of its argument
Example
In this example a ClassCastException would be thrown because the object o is cast without check. The equals(Object) method should never throw any exception as this violates the contract.
public boolean equals(Object obj) {
EqualsAssume toCompare = (EqualsAssume)obj;
...
}
Suppression
This warning can be suppressed with @SuppressFBWarnings(value="BC_EQUALS_METHOD_SHOULD_WORK_FOR_ALL_OBJECTS").
Project examples
- Detected EqualsAssume Line 27
- Suppressed SuppressEqualsAssume Line 27
BIT: Check for sign of bitwise operation
Example
In this example the check ((value & FLAG) > 0) will fail when FLAG is a negative value (e.g. 0x80000000). Then the result will be also negative and the check will fail.
private static final int FLAG = 0x40000000;
public boolean bug(int value) {
boolean flagSet = ((value & FLAG) > 0);
...
}
Restrictions
This bug will not be found when the FLAG is already negative (the highest significant bit is set).
private static final int HIGHEST_FLAG = 0x80000000;
public boolean highestBitBug(int value) {
boolean flagSet = ((value & HIGHEST_FLAG) > 0);
...
}
Project examples
- Detected CheckSign Line 31
- Not Detected CheckSign Line 36
- Suppressed CheckSign Line 40
CN: Class implements Cloneable but does not define or use clone method
Example
In this example the created class does not override the clone() method.
public class NoClone implements Cloneable {
// no clone()
}
Project examples
- Detected NoClone Line 22
- Suppressed SuppressNoClone Line 24
CN: clone method does not call super.clone()
Example
In this example the created class does not call the clone() method of the super class. Every class that implements the Cloneable must call the method super.clone() to ensure that the clone() returns the correct class.
public Object clone() throws CloneNotSupportedException {
// no call to super.clone();
}
Suppression
This warning can be suppressed with @SuppressFBWarnings(value="CN_IDIOM_NO_SUPER_CALL").
Project examples
- Detected NoSuperClone Line 26
- Suppressed SuppressNoSuperClone Line 26
CN: Class defines clone() but doesn’t implement Cloneable
Example
In this example the created class overrides the method clone() but does not implement the interface Cloneable. This is at least uncommon and not expected.
public class NoCloneable {
public Object clone() throws CloneNotSupportedException {
...
}
}
Suppression
This warning can be suppressed with @SuppressFBWarnings(value="CN_IMPLEMENTS_CLONE_BUT_NOT_CLONEABLE").
Project examples
- Detected NoCloneable Line 26
- Suppressed SuppressNoCloneable Line 24
Co: Abstract class defines covariant compareTo() method
Example
In this example the class Covariant implements the interface Comparable and implements the method compareTo with itself as argument. This is problematic as subclasses cannot override this method with another argument.
public abstract class Covariant implements Comparable<Covariant> {
@Override
public abstract int compareTo(Covariant o);
}
Project examples
- Detected Covariant Line 22
- Suppressed SuppressCovariant Line 24