https://github.com/google/guava/guava: Guava is a suite of core and expanded libraries that include utility classes, google's collections, io classes, and much much more. 
/*
 * Copyright (C) 2007 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.base;

import static com.google.common.base.Preconditions.checkNotNull;
import static java.util.Arrays.asList;
import static java.util.Collections.unmodifiableList;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.VisibleForTesting;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.io.IOException;
import java.io.PrintWriter;
import java.io.StringWriter;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.AbstractList;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import org.checkerframework.checker.nullness.qual.Nullable;


Static utility methods pertaining to instances of Throwable. 
See the Guava User Guide entry on Throwables.

Author:Kevin Bourrillion, Ben Yu
Since:1.0
/**
 * Static utility methods pertaining to instances of {@link Throwable}.
 *
 * <p>See the Guava User Guide entry on <a
 * href="https://github.com/google/guava/wiki/ThrowablesExplained">Throwables</a>.
 *
 * @author Kevin Bourrillion
 * @author Ben Yu
 * @since 1.0
 */
@GwtCompatible(emulated = true)
public final class Throwables {
  private Throwables() {}

  
Throws throwable if it is an instance of declaredType. Example usage: 
for (Foo foo : foos) {
  try {
    foo.bar();
  } catch (BarException | RuntimeException | Error t) {
    failure = t;
  }
}
if (failure != null) {
  throwIfInstanceOf(failure, BarException.class);
  throwIfUnchecked(failure);
  throw new AssertionError(failure);
}



Since:20.0
/**
   * Throws {@code throwable} if it is an instance of {@code declaredType}. Example usage:
   *
   * <pre>
   * for (Foo foo : foos) {
   *   try {
   *     foo.bar();
   *   } catch (BarException | RuntimeException | Error t) {
   *     failure = t;
   *   }
   * }
   * if (failure != null) {
   *   throwIfInstanceOf(failure, BarException.class);
   *   throwIfUnchecked(failure);
   *   throw new AssertionError(failure);
   * }
   * </pre>
   *
   * @since 20.0
   */
  @GwtIncompatible // Class.cast, Class.isInstance
  public static <X extends Throwable> void throwIfInstanceOf(
      Throwable throwable, Class<X> declaredType) throws X {
    checkNotNull(throwable);
    if (declaredType.isInstance(throwable)) {
      throw declaredType.cast(throwable);
    }
  }

  
Propagates throwable exactly as-is, if and only if it is an instance of 
declaredType. Example usage: 
try {
  someMethodThatCouldThrowAnything();
} catch (IKnowWhatToDoWithThisException e) {
  handle(e);
} catch (Throwable t) {
  Throwables.propagateIfInstanceOf(t, IOException.class);
  Throwables.propagateIfInstanceOf(t, SQLException.class);
  throw Throwables.propagate(t);
}



Deprecated:Use throwIfInstanceOf, which has the same behavior but rejects 
    null.
/**
   * Propagates {@code throwable} exactly as-is, if and only if it is an instance of {@code
   * declaredType}. Example usage:
   *
   * <pre>
   * try {
   *   someMethodThatCouldThrowAnything();
   * } catch (IKnowWhatToDoWithThisException e) {
   *   handle(e);
   * } catch (Throwable t) {
   *   Throwables.propagateIfInstanceOf(t, IOException.class);
   *   Throwables.propagateIfInstanceOf(t, SQLException.class);
   *   throw Throwables.propagate(t);
   * }
   * </pre>
   *
   * @deprecated Use {@link #throwIfInstanceOf}, which has the same behavior but rejects {@code
   *     null}.
   */
  @Deprecated
  @GwtIncompatible // throwIfInstanceOf
  public static <X extends Throwable> void propagateIfInstanceOf(
      @Nullable Throwable throwable, Class<X> declaredType) throws X {
    if (throwable != null) {
      throwIfInstanceOf(throwable, declaredType);
    }
  }

  
Throws throwable if it is a RuntimeException or Error. Example usage: 
for (Foo foo : foos) {
  try {
    foo.bar();
  } catch (RuntimeException | Error t) {
    failure = t;
  }
}
if (failure != null) {
  throwIfUnchecked(failure);
  throw new AssertionError(failure);
}



Since:20.0
/**
   * Throws {@code throwable} if it is a {@link RuntimeException} or {@link Error}. Example usage:
   *
   * <pre>
   * for (Foo foo : foos) {
   *   try {
   *     foo.bar();
   *   } catch (RuntimeException | Error t) {
   *     failure = t;
   *   }
   * }
   * if (failure != null) {
   *   throwIfUnchecked(failure);
   *   throw new AssertionError(failure);
   * }
   * </pre>
   *
   * @since 20.0
   */
  public static void throwIfUnchecked(Throwable throwable) {
    checkNotNull(throwable);
    if (throwable instanceof RuntimeException) {
      throw (RuntimeException) throwable;
    }
    if (throwable instanceof Error) {
      throw (Error) throwable;
    }
  }

  
Propagates throwable exactly as-is, if and only if it is an instance of RuntimeException or Error. Example usage: 
try {
  someMethodThatCouldThrowAnything();
} catch (IKnowWhatToDoWithThisException e) {
  handle(e);
} catch (Throwable t) {
  Throwables.propagateIfPossible(t);
  throw new RuntimeException("unexpected", t);
}



Deprecated:Use throwIfUnchecked, which has the same behavior but rejects 
    null.
/**
   * Propagates {@code throwable} exactly as-is, if and only if it is an instance of {@link
   * RuntimeException} or {@link Error}. Example usage:
   *
   * <pre>
   * try {
   *   someMethodThatCouldThrowAnything();
   * } catch (IKnowWhatToDoWithThisException e) {
   *   handle(e);
   * } catch (Throwable t) {
   *   Throwables.propagateIfPossible(t);
   *   throw new RuntimeException("unexpected", t);
   * }
   * </pre>
   *
   * @deprecated Use {@link #throwIfUnchecked}, which has the same behavior but rejects {@code
   *     null}.
   */
  @Deprecated
  @GwtIncompatible
  public static void propagateIfPossible(@Nullable Throwable throwable) {
    if (throwable != null) {
      throwIfUnchecked(throwable);
    }
  }

  
Propagates throwable exactly as-is, if and only if it is an instance of RuntimeException, Error, or declaredType. Example usage: 
try {
  someMethodThatCouldThrowAnything();
} catch (IKnowWhatToDoWithThisException e) {
  handle(e);
} catch (Throwable t) {
  Throwables.propagateIfPossible(t, OtherException.class);
  throw new RuntimeException("unexpected", t);
}



Params:
  • throwable – the Throwable to possibly propagate
  • declaredType – the single checked exception type declared by the calling method
/**
   * Propagates {@code throwable} exactly as-is, if and only if it is an instance of {@link
   * RuntimeException}, {@link Error}, or {@code declaredType}. Example usage:
   *
   * <pre>
   * try {
   *   someMethodThatCouldThrowAnything();
   * } catch (IKnowWhatToDoWithThisException e) {
   *   handle(e);
   * } catch (Throwable t) {
   *   Throwables.propagateIfPossible(t, OtherException.class);
   *   throw new RuntimeException("unexpected", t);
   * }
   * </pre>
   *
   * @param throwable the Throwable to possibly propagate
   * @param declaredType the single checked exception type declared by the calling method
   */
  @GwtIncompatible // propagateIfInstanceOf
  public static <X extends Throwable> void propagateIfPossible(
      @Nullable Throwable throwable, Class<X> declaredType) throws X {
    propagateIfInstanceOf(throwable, declaredType);
    propagateIfPossible(throwable);
  }

  
Propagates throwable exactly as-is, if and only if it is an instance of RuntimeException, Error, declaredType1, or declaredType2. In the unlikely case that you have three or more declared checked exception types, you can handle them all by invoking these methods repeatedly. See usage example in propagateIfPossible(Throwable, Class<RuntimeException>). 
Params:
  • throwable – the Throwable to possibly propagate
  • declaredType1 – any checked exception type declared by the calling method
  • declaredType2 – any other checked exception type declared by the calling method
/**
   * Propagates {@code throwable} exactly as-is, if and only if it is an instance of {@link
   * RuntimeException}, {@link Error}, {@code declaredType1}, or {@code declaredType2}. In the
   * unlikely case that you have three or more declared checked exception types, you can handle them
   * all by invoking these methods repeatedly. See usage example in {@link
   * #propagateIfPossible(Throwable, Class)}.
   *
   * @param throwable the Throwable to possibly propagate
   * @param declaredType1 any checked exception type declared by the calling method
   * @param declaredType2 any other checked exception type declared by the calling method
   */
  @GwtIncompatible // propagateIfInstanceOf
  public static <X1 extends Throwable, X2 extends Throwable> void propagateIfPossible(
      @Nullable Throwable throwable, Class<X1> declaredType1, Class<X2> declaredType2)
      throws X1, X2 {
    checkNotNull(declaredType2);
    propagateIfInstanceOf(throwable, declaredType1);
    propagateIfPossible(throwable, declaredType2);
  }

  
Propagates throwable as-is if it is an instance of RuntimeException or Error, or else as a last resort, wraps it in a RuntimeException and then propagates. 
This method always throws an exception. The RuntimeException return type allows client code to signal to the compiler that statements after the call are unreachable. Example usage: 
T doSomething() {
  try {
    return someMethodThatCouldThrowAnything();
  } catch (IKnowWhatToDoWithThisException e) {
    return handle(e);
  } catch (Throwable t) {
    throw Throwables.propagate(t);
  }
}



Params:
  • throwable – the Throwable to propagate
Returns:nothing will ever be returned; this return type is only for your convenience, as
    illustrated in the example above
Deprecated:Use throw e or throw new RuntimeException(e) directly, or use a combination of throwIfUnchecked and throw new RuntimeException(e). For background on the deprecation, read Why we deprecated Throwables.propagate.
/**
   * Propagates {@code throwable} as-is if it is an instance of {@link RuntimeException} or {@link
   * Error}, or else as a last resort, wraps it in a {@code RuntimeException} and then propagates.
   *
   * <p>This method always throws an exception. The {@code RuntimeException} return type allows
   * client code to signal to the compiler that statements after the call are unreachable. Example
   * usage:
   *
   * <pre>
   * T doSomething() {
   *   try {
   *     return someMethodThatCouldThrowAnything();
   *   } catch (IKnowWhatToDoWithThisException e) {
   *     return handle(e);
   *   } catch (Throwable t) {
   *     throw Throwables.propagate(t);
   *   }
   * }
   * </pre>
   *
   * @param throwable the Throwable to propagate
   * @return nothing will ever be returned; this return type is only for your convenience, as
   *     illustrated in the example above
   * @deprecated Use {@code throw e} or {@code throw new RuntimeException(e)} directly, or use a
   *     combination of {@link #throwIfUnchecked} and {@code throw new RuntimeException(e)}. For
   *     background on the deprecation, read <a href="https://goo.gl/Ivn2kc">Why we deprecated
   *     {@code Throwables.propagate}</a>.
   */
  @CanIgnoreReturnValue
  @GwtIncompatible
  @Deprecated
  public static RuntimeException propagate(Throwable throwable) {
    throwIfUnchecked(throwable);
    throw new RuntimeException(throwable);
  }

  
Returns the innermost cause of throwable. The first throwable in a chain provides context from when the error or exception was initially detected. Example usage: 
assertEquals("Unable to assign a customer id", Throwables.getRootCause(e).getMessage());



Throws:
/**
   * Returns the innermost cause of {@code throwable}. The first throwable in a chain provides
   * context from when the error or exception was initially detected. Example usage:
   *
   * <pre>
   * assertEquals("Unable to assign a customer id", Throwables.getRootCause(e).getMessage());
   * </pre>
   *
   * @throws IllegalArgumentException if there is a loop in the causal chain
   */
  public static Throwable getRootCause(Throwable throwable) {
    // Keep a second pointer that slowly walks the causal chain. If the fast pointer ever catches
    // the slower pointer, then there's a loop.
    Throwable slowPointer = throwable;
    boolean advanceSlowPointer = false;

    Throwable cause;
    while ((cause = throwable.getCause()) != null) {
      throwable = cause;

      if (throwable == slowPointer) {
        throw new IllegalArgumentException("Loop in causal chain detected.", throwable);
      }
      if (advanceSlowPointer) {
        slowPointer = slowPointer.getCause();
      }
      advanceSlowPointer = !advanceSlowPointer; // only advance every other iteration
    }
    return throwable;
  }

  
Gets a Throwable cause chain as a list. The first entry in the list will be 
throwable followed by its cause hierarchy. Note that this is a snapshot of the cause chain and will not reflect any subsequent changes to the cause chain. 
Here's an example of how it can be used to find specific types of exceptions in the cause
chain:

Iterables.filter(Throwables.getCausalChain(e), IOException.class));



Params:
  • throwable – the non-null Throwable to extract causes from
Throws:
Returns:an unmodifiable list containing the cause chain starting with throwable
/**
   * Gets a {@code Throwable} cause chain as a list. The first entry in the list will be {@code
   * throwable} followed by its cause hierarchy. Note that this is a snapshot of the cause chain and
   * will not reflect any subsequent changes to the cause chain.
   *
   * <p>Here's an example of how it can be used to find specific types of exceptions in the cause
   * chain:
   *
   * <pre>
   * Iterables.filter(Throwables.getCausalChain(e), IOException.class));
   * </pre>
   *
   * @param throwable the non-null {@code Throwable} to extract causes from
   * @return an unmodifiable list containing the cause chain starting with {@code throwable}
   * @throws IllegalArgumentException if there is a loop in the causal chain
   */
  @Beta // TODO(kevinb): decide best return type
  public static List<Throwable> getCausalChain(Throwable throwable) {
    checkNotNull(throwable);
    List<Throwable> causes = new ArrayList<>(4);
    causes.add(throwable);

    // Keep a second pointer that slowly walks the causal chain. If the fast pointer ever catches
    // the slower pointer, then there's a loop.
    Throwable slowPointer = throwable;
    boolean advanceSlowPointer = false;

    Throwable cause;
    while ((cause = throwable.getCause()) != null) {
      throwable = cause;
      causes.add(throwable);

      if (throwable == slowPointer) {
        throw new IllegalArgumentException("Loop in causal chain detected.", throwable);
      }
      if (advanceSlowPointer) {
        slowPointer = slowPointer.getCause();
      }
      advanceSlowPointer = !advanceSlowPointer; // only advance every other iteration
    }
    return Collections.unmodifiableList(causes);
  }

  
Returns throwable's cause, cast to expectedCauseType. 
Prefer this method instead of manually casting an exception's cause. For example, 
(IOException) e.getCause() throws a ClassCastException that discards the original exception e if the cause is not an IOException, but 
Throwables.getCauseAs(e, IOException.class) keeps e as the ClassCastException's cause. 
Throws:
  • ClassCastException – if the cause cannot be cast to the expected type. The 
    ClassCastException's cause is throwable.
Since:22.0
/**
   * Returns {@code throwable}'s cause, cast to {@code expectedCauseType}.
   *
   * <p>Prefer this method instead of manually casting an exception's cause. For example, {@code
   * (IOException) e.getCause()} throws a {@link ClassCastException} that discards the original
   * exception {@code e} if the cause is not an {@link IOException}, but {@code
   * Throwables.getCauseAs(e, IOException.class)} keeps {@code e} as the {@link
   * ClassCastException}'s cause.
   *
   * @throws ClassCastException if the cause cannot be cast to the expected type. The {@code
   *     ClassCastException}'s cause is {@code throwable}.
   * @since 22.0
   */
  @Beta
  @GwtIncompatible // Class.cast(Object)
  public static <X extends Throwable> X getCauseAs(
      Throwable throwable, Class<X> expectedCauseType) {
    try {
      return expectedCauseType.cast(throwable.getCause());
    } catch (ClassCastException e) {
      e.initCause(throwable);
      throw e;
    }
  }

  
Returns a string containing the result of toString(), followed by the full, recursive stack trace of throwable. Note that you probably should not be parsing the resulting string; if you need programmatic access to the stack frames, you can call Throwable.getStackTrace(). 
/**
   * Returns a string containing the result of {@link Throwable#toString() toString()}, followed by
   * the full, recursive stack trace of {@code throwable}. Note that you probably should not be
   * parsing the resulting string; if you need programmatic access to the stack frames, you can call
   * {@link Throwable#getStackTrace()}.
   */
  @GwtIncompatible // java.io.PrintWriter, java.io.StringWriter
  public static String getStackTraceAsString(Throwable throwable) {
    StringWriter stringWriter = new StringWriter();
    throwable.printStackTrace(new PrintWriter(stringWriter));
    return stringWriter.toString();
  }

  
Returns the stack trace of throwable, possibly providing slower iteration over the full trace but faster iteration over parts of the trace. Here, "slower" and "faster" are defined in comparison to the normal way to access the stack trace, 
throwable.getStackTrace(). Note, however, that this method's special implementation is not available for all platforms and configurations. If that implementation is unavailable, this method falls back to getStackTrace. Callers that require the special implementation can check its availability with lazyStackTraceIsLazy(). 
The expected (but not guaranteed) performance of the special implementation differs from getStackTrace in one main way: The lazyStackTrace call itself returns quickly by delaying the per-stack-frame work until each element is accessed. Roughly speaking: 
    
  
  • getStackTrace takes stackSize time to return but then negligible time to retrieve each element of the returned list. 
  • lazyStackTrace takes negligible time to return but then 1/stackSize time to retrieve each element of the returned list (probably slightly more than 
      1/stackSize). 


Note: The special implementation does not respect calls to 
throwable.setStackTrace. Instead, it always reflects the original stack trace from the exception's creation. 
Since:19.0
/**
   * Returns the stack trace of {@code throwable}, possibly providing slower iteration over the full
   * trace but faster iteration over parts of the trace. Here, "slower" and "faster" are defined in
   * comparison to the normal way to access the stack trace, {@link Throwable#getStackTrace()
   * throwable.getStackTrace()}. Note, however, that this method's special implementation is not
   * available for all platforms and configurations. If that implementation is unavailable, this
   * method falls back to {@code getStackTrace}. Callers that require the special implementation can
   * check its availability with {@link #lazyStackTraceIsLazy()}.
   *
   * <p>The expected (but not guaranteed) performance of the special implementation differs from
   * {@code getStackTrace} in one main way: The {@code lazyStackTrace} call itself returns quickly
   * by delaying the per-stack-frame work until each element is accessed. Roughly speaking:
   *
   * <ul>
   *   <li>{@code getStackTrace} takes {@code stackSize} time to return but then negligible time to
   *       retrieve each element of the returned list.
   *   <li>{@code lazyStackTrace} takes negligible time to return but then {@code 1/stackSize} time
   *       to retrieve each element of the returned list (probably slightly more than {@code
   *       1/stackSize}).
   * </ul>
   *
   * <p>Note: The special implementation does not respect calls to {@link Throwable#setStackTrace
   * throwable.setStackTrace}. Instead, it always reflects the original stack trace from the
   * exception's creation.
   *
   * @since 19.0
   */
  // TODO(cpovirk): Say something about the possibility that List access could fail at runtime?
  @Beta
  @GwtIncompatible // lazyStackTraceIsLazy, jlaStackTrace
  // TODO(cpovirk): Consider making this available under GWT (slow implementation only).
  public static List<StackTraceElement> lazyStackTrace(Throwable throwable) {
    return lazyStackTraceIsLazy()
        ? jlaStackTrace(throwable)
        : unmodifiableList(asList(throwable.getStackTrace()));
  }

  
Returns whether lazyStackTrace will use the special implementation described in its documentation. 
Since:19.0
/**
   * Returns whether {@link #lazyStackTrace} will use the special implementation described in its
   * documentation.
   *
   * @since 19.0
   */
  @Beta
  @GwtIncompatible // getStackTraceElementMethod
  public static boolean lazyStackTraceIsLazy() {
    return getStackTraceElementMethod != null && getStackTraceDepthMethod != null;
  }

  @GwtIncompatible // invokeAccessibleNonThrowingMethod
  private static List<StackTraceElement> jlaStackTrace(final Throwable t) {
    checkNotNull(t);
    /*
     * TODO(cpovirk): Consider optimizing iterator() to catch IOOBE instead of doing bounds checks.
     *
     * TODO(cpovirk): Consider the UnsignedBytes pattern if it performs faster and doesn't cause
     * AOSP grief.
     */
    return new AbstractList<StackTraceElement>() {
      @Override
      public StackTraceElement get(int n) {
        return (StackTraceElement)
            invokeAccessibleNonThrowingMethod(getStackTraceElementMethod, jla, t, n);
      }

      @Override
      public int size() {
        return (Integer) invokeAccessibleNonThrowingMethod(getStackTraceDepthMethod, jla, t);
      }
    };
  }

  @GwtIncompatible // java.lang.reflect
  private static Object invokeAccessibleNonThrowingMethod(
      Method method, Object receiver, Object... params) {
    try {
      return method.invoke(receiver, params);
    } catch (IllegalAccessException e) {
      throw new RuntimeException(e);
    } catch (InvocationTargetException e) {
      throw propagate(e.getCause());
    }
  }

  
JavaLangAccess class name to load using reflection 
/** JavaLangAccess class name to load using reflection */
  @GwtIncompatible // not used by GWT emulation
  private static final String JAVA_LANG_ACCESS_CLASSNAME = "sun.misc.JavaLangAccess";

  
SharedSecrets class name to load using reflection 
/** SharedSecrets class name to load using reflection */
  @GwtIncompatible // not used by GWT emulation
  @VisibleForTesting
  static final String SHARED_SECRETS_CLASSNAME = "sun.misc.SharedSecrets";

  
Access to some fancy internal JVM internals. 
/** Access to some fancy internal JVM internals. */
  @GwtIncompatible // java.lang.reflect
  private static final @Nullable Object jla = getJLA();

  
The "getStackTraceElementMethod" method, only available on some JDKs so we use reflection to
find it when available. When this is null, use the slow way.

/**
   * The "getStackTraceElementMethod" method, only available on some JDKs so we use reflection to
   * find it when available. When this is null, use the slow way.
   */
  @GwtIncompatible // java.lang.reflect
  private static final @Nullable Method getStackTraceElementMethod =
      (jla == null) ? null : getGetMethod();

  
The "getStackTraceDepth" method, only available on some JDKs so we use reflection to find it
when available. When this is null, use the slow way.

/**
   * The "getStackTraceDepth" method, only available on some JDKs so we use reflection to find it
   * when available. When this is null, use the slow way.
   */
  @GwtIncompatible // java.lang.reflect
  private static final @Nullable Method getStackTraceDepthMethod =
      (jla == null) ? null : getSizeMethod();

  
Returns the JavaLangAccess class that is present in all Sun JDKs. It is not whitelisted for
AppEngine, and not present in non-Sun JDKs.

/**
   * Returns the JavaLangAccess class that is present in all Sun JDKs. It is not whitelisted for
   * AppEngine, and not present in non-Sun JDKs.
   */
  @GwtIncompatible // java.lang.reflect
  private static @Nullable Object getJLA() {
    try {
      /*
       * We load sun.misc.* classes using reflection since Android doesn't support these classes and
       * would result in compilation failure if we directly refer to these classes.
       */
      Class<?> sharedSecrets = Class.forName(SHARED_SECRETS_CLASSNAME, false, null);
      Method langAccess = sharedSecrets.getMethod("getJavaLangAccess");
      return langAccess.invoke(null);
    } catch (ThreadDeath death) {
      throw death;
    } catch (Throwable t) {
      /*
       * This is not one of AppEngine's whitelisted classes, so even in Sun JDKs, this can fail with
       * a NoClassDefFoundError. Other apps might deny access to sun.misc packages.
       */
      return null;
    }
  }

  
Returns the Method that can be used to resolve an individual StackTraceElement, or null if that
method cannot be found (it is only to be found in fairly recent JDKs).

/**
   * Returns the Method that can be used to resolve an individual StackTraceElement, or null if that
   * method cannot be found (it is only to be found in fairly recent JDKs).
   */
  @GwtIncompatible // java.lang.reflect
  private static @Nullable Method getGetMethod() {
    return getJlaMethod("getStackTraceElement", Throwable.class, int.class);
  }

  
Returns the Method that can be used to return the size of a stack, or null if that method cannot be found (it is only to be found in fairly recent JDKs). Tries to test method JavaLangAccess.getStackTraceDepth(Throwable) getStackTraceDepth} prior to return it (might fail some JDKs). 
See Throwables#lazyStackTrace throws
UnsupportedOperationException.

/**
   * Returns the Method that can be used to return the size of a stack, or null if that method
   * cannot be found (it is only to be found in fairly recent JDKs). Tries to test method {@link
   * sun.misc.JavaLangAccess#getStackTraceDepth(Throwable)} getStackTraceDepth} prior to return it
   * (might fail some JDKs).
   *
   * <p>See <a href="https://github.com/google/guava/issues/2887">Throwables#lazyStackTrace throws
   * UnsupportedOperationException</a>.
   */
  @GwtIncompatible // java.lang.reflect
  private static @Nullable Method getSizeMethod() {
    try {
      Method getStackTraceDepth = getJlaMethod("getStackTraceDepth", Throwable.class);
      if (getStackTraceDepth == null) {
        return null;
      }
      getStackTraceDepth.invoke(getJLA(), new Throwable());
      return getStackTraceDepth;
    } catch (UnsupportedOperationException | IllegalAccessException | InvocationTargetException e) {
      return null;
    }
  }

  @GwtIncompatible // java.lang.reflect
  private static @Nullable Method getJlaMethod(String name, Class<?>... parameterTypes)
      throws ThreadDeath {
    try {
      return Class.forName(JAVA_LANG_ACCESS_CLASSNAME, false, null).getMethod(name, parameterTypes);
    } catch (ThreadDeath death) {
      throw death;
    } catch (Throwable t) {
      /*
       * Either the JavaLangAccess class itself is not found, or the method is not supported on the
       * JVM.
       */
      return null;
    }
  }
}