JDK 14 の新機能 JEP 358: Helpful NullPointerExceptions を試した

-XX:+ShowCodeDetailsInExceptionMessages を追加する必要がある。

import static org.assertj.core.api.Assertions.assertThat;

import java.lang.management.ManagementFactory;
import java.lang.management.RuntimeMXBean;

import org.junit.Test;

public class NPETest {
    public String maybeNull = null;

    @Test
    public void testNpe() {
        // Preconditions
        final RuntimeMXBean runtimeMXBean = ManagementFactory.getRuntimeMXBean();
        assertThat(runtimeMXBean.getSpecVersion()).isEqualTo("14");
        assertThat(runtimeMXBean.getInputArguments()).contains("-XX:+ShowCodeDetailsInExceptionMessages");

        // Do
        final String subst = maybeNull.substring(0, 1);
    }
}

これで

java.lang.NullPointerException: Cannot invoke "String.substring(int, int)" because "this.maybeNull" is null

時代は変わるなぁ。。。