Useless unboxing of a value JAVA-W1052

A boxed value is unboxed and then immediately reboxed. This has likely occurred due to an unboxing operation by the programmer, which the java compiler has undone.

Bad Practice

public void acceptsInteger(Integer x) { ... }

Integer a = 0;
Float b = 1f;

// Same type, unboxed.
acceptsInteger(a.intValue());

// Different type, unboxed.
acceptsInteger(b.intValue());

The bytecode for the first call would look something like:

aload_1                           // Load `a` into memory.
invokevirtual #13                 // Call instance method `Integer.intValue()` on `a`
invokestatic  #7                  // Call static method `Integer.valueOf()` with the result of `intValue()`
invokestatic  #23                 // Call instance method `acceptsInteger()`

Note two contradicting method calls: this code calls Integer.intValue() immediately followed by Integer.valueOf().

Recommended

If a method expects a boxed type, it is better to provide it a value that is of the same type than to give it one of a different one.

acceptsInteger(a);