Java Null Risk Example

NullRisk.java

// Java null risk workaround example
// Kotlin null safe example https://gist.github.com/gaplo917/77d7ee9f48ed20f4a60bc20a1b39a2e6

import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;

import java.util.Optional;
import static java.lang.System.*;

class NullRisk {
  // Bad code in Java
  public String doRiskyThing(String str){
    return str.toLowerCase();
  }
  
  // Human error by typing wrong annotation, should be @NotNull
  public String doMissLeadingThing(@Nullable String str){
    return str.toLowerCase(); // IDE warning
  }
  
  // possible work around, IDE will show warning if the input is null
  // but it is safe to compile
  @NotNull
  public String doSafeThing(@NotNull String str){
    return str.toLowerCase();
  }

  // possible work around, but using Optional in java is pain and not handy as Kotlin/Scala
  public Optional<String> doOptionalThing(@Nullable String strOpt){
    return Optional.ofNullable(strOpt).map(String::toLowerCase);
  }

  {
    // compile OK! throw NullPointerException in run-time
    out.println(doRiskyThing(null));
    
    // compile OK! IDE warning, throw NullPointerException in run-time
    out.println(doSafeThing(null)); 
    
    // compile OK! throw NullPointerException in run-time
    out.println(doMissLeadingThing(null));
    
    // compile OK!
    out.println(doOptionalThing(null));
  }
}