Why is this an issue?

Creating temporary primitive wrapper objects only for String conversion or the use of the compareTo() method is inefficient.

Instead, the static toString() or compare() method of the primitive wrapper class should be used.

Noncompliant code example

private int isZero(int value){
    return Integer.valueOf(value).compareTo(0); // Noncompliant
}
private String convert(int value){
    return Integer.valueOf(value).toString(); // Noncompliant
}

Compliant solution

private int isZero(int value){
    return Integer.compare(value, 0); // Compliant
}
private String convert(int value){
    return Integer.toString(value); // Compliant
}