JAVA.CLASS.CAST : Risky Class Cast (Java)

Summary

A classcast might be incorrect at runtime.

• If JAVA_ANALYSIS_PEDANTIC_MODE=Yes, checks for this warning class will cover casts on:
  • formal parameters of entry methods,
  • method return values, and
  • fields.
  A warning is issued if the analysis cannot infer that the cast is safe. This includes the case where the analysis can infer that the cast is unsafe, as well as the case where it cannot reach a definite conclusion either way.

  You can annotate a method as predictable — that is, as always returning a type predictable by software developers — with the @com.juliasoft.julia.checkers.classcast.PredictableReturnType annotation. The analysis will not issue warnings for any casts of return values from methods with this annotation.

• If JAVA_ANALYSIS_PEDANTIC_MODE=No, checks for this warning class will cover only casts on formal parameters of entry methods. A warning is issued only if the analysis can infer that the cast is unsafe.

  @com.juliasoft.julia.checkers.classcast.PredictableReturnType annotations have no effect in this case, since checks do not cover casts on method return values.

(Note that entry methods are determined with respect to the setting of JAVA_ANALYSIS_ENTRY_POINTS_MODE.)

Java checks explicit type downcasts at runtime. If they do not hold, a runtime exception is thrown. This checker verifies that casts will be satisfied at runtime, so that they will never throw an exception.

Properties

WARNING_FILTER += discard class="Risky Class Cast (Java)"

Example

public class TestCasts {
  private Object f;
  private Object g = "hi";

  public void m1(Object o) {
    if (((String) o).startsWith("hello"))       // "Risky Class Cast (Java)" warning issued here
      System.out.println("nice to meet you");
  }

  public void m2(String s, Object o) {
    if (((String) o).startsWith("hello"))       // "Risky Class Cast (Java)" warning issued here
      System.out.println("nice to meet you");
  }

  public void m3(String s, Object o) {
    if (((String) wrap(o)).startsWith("hello")) // "Risky Class Cast (Java)" warning issued here if JAVA_ANALYSIS_PEDANTIC_MODE=Yes
      System.out.println("nice to meet you");
  }

  public void m4() {
    if (((String) f).startsWith("hello"))       // "Risky Class Cast (Java)" warning issued here if JAVA_ANALYSIS_PEDANTIC_MODE=Yes
      System.out.println("nice to meet you");
  }

  public void m5() {
    if (((String) g).startsWith("hello"))                    // ok: safe cast
      System.out.println("nice to meet you");
  }

  private Object wrap(Object o) {
    return o;
  }

  public void caller1() {
    m1("hi");
    m1(this);
  }

  public void caller2() {
    m2("ciao", "hello");
    m2("come stai", "how are you?");
  }

  public void caller3() {
    m3("ciao", "hello");
    m3("come stai", f = new Object());
  }
}

Resolution

For each classcast warning, verify that all types that will ever reach that program point are assignable to the type used for the cast.

Relevant Configuration File Parameters

The following configuration file parameters affect checks for this warning class.

• JAVA_ANALYSIS_PEDANTIC_MODE
• REPORT_SIMILAR_WARNINGS
• WARNING_FILTER