# How can i use mutate in Java Client

**URL:** <https://forums.foundationdb.org/t/how-can-i-use-mutate-in-java-client/3560>\
**Category:** Using FoundationDB\
**Tags:** bindings\
**Created:** [September 23, 2022, 7:07am UTC](https://forums.foundationdb.org/t/how-can-i-use-mutate-in-java-client/3560 "2022-09-23T07:07:20Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![T-TRz879](https://sea1.discourse-cdn.com/foundationdb/user_avatar/forums.foundationdb.org/t-trz879/32/1418_2.png) [@T-TRz879](https://forums.foundationdb.org/u/T-TRz879)\
**Post date:** [September 23, 2022, 7:07am UTC](https://forums.foundationdb.org/t/how-can-i-use-mutate-in-java-client/3560/1 "2022-09-23T07:07:21Z")

</div>

i want to code cas operation in mutate

```auto
  public void testCAS() throws InterruptedException {
    Database db = fdb.open();
    try (Transaction tr = db.createTransaction()) {
      tr.clear(Tuple.from("count").pack());
      tr.commit().join();
    }
    CountDownLatch countDownLatch = new CountDownLatch(10);
    for (int i = 0; i < 10; i++) {
      new Thread(
              () -> {
                db.run(
                    tr -> {
                      incrementCounter1(tr);
                      return null;
                    });
                countDownLatch.countDown();
              })
          .start();
    }
    countDownLatch.await();
    try (Transaction tr1 = db.createTransaction()) {
      byte[] join = tr1.snapshot().get(Tuple.from("count").pack()).join();
      System.out.println(Tuple.fromBytes(join).getLong(0));
    }
  }

  private void incrementCounter1(Transaction tr) {
    byte[] join = tr.snapshot().get(Tuple.from("count").pack()).join();
    long counterValue = 0;
    if (join != null) {
      counterValue = Tuple.fromBytes(join).getLong(0);
    }
    tr.mutate(MutationType.ADD, Tuple.from("count").pack(), Tuple.from(counterValue + 1).pack());
  }

```

Actually,I have some problems…  
Finally, I want to get the value of count, but the returned byte array is [-46,10]

```auto
java.lang.IllegalArgumentException: Unknown tuple data type -46 at index 0

	at com.apple.foundationdb.tuple.TupleUtil.decode(TupleUtil.java:588)
	at com.apple.foundationdb.tuple.TupleUtil.unpack(TupleUtil.java:676)
	at com.apple.foundationdb.tuple.Tuple.fromBytes(Tuple.java:552)
	at com.apple.foundationdb.tuple.Tuple.fromBytes(Tuple.java:527)
	at com.trz.CRUDTest.testCAS(CRUDTest.java:229)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:271)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:160)
	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:69)
	at com.intellij.rt.junit.IdeaTestRunner$Repeater$1.execute(IdeaTestRunner.java:38)
	at com.intellij.rt.execution.junit.TestsRepeater.repeat(TestsRepeater.java:11)
	at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:35)
	at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:235)
	at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:54)

```

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<div class="post-metadata">

**Author:** ![MMcM](https://avatars.discourse-cdn.com/v4/letter/m/d07c76/32.png) [@MMcM](https://forums.foundationdb.org/u/MMcM)\
**Post date:** [September 23, 2022, 4:34pm UTC](https://forums.foundationdb.org/t/how-can-i-use-mutate-in-java-client/3560/2 "2022-09-23T16:34:47Z")

</div>

`MutationType.ADD` [Javadoc](https://apple.github.io/foundationdb/javadoc/com/apple/foundationdb/MutationType.html#ADD):

> Performs an addition of little-endian integers.

There is no atomic mutation for Tuple-encoded integers.

---

<div class="post-metadata">

**Author:** ![alloc](https://sea1.discourse-cdn.com/foundationdb/user_avatar/forums.foundationdb.org/alloc/32/9_2.png) [@alloc](https://forums.foundationdb.org/u/alloc)\
**Post date:** [September 26, 2022, 3:29pm UTC](https://forums.foundationdb.org/t/how-can-i-use-mutate-in-java-client/3560/3 "2022-09-26T15:29:51Z")

</div>

You can see an example of how to use the ADD mutation in the `multimap` sample code: [Multimaps — FoundationDB 7.1](https://apple.github.io/foundationdb/multimaps-java.html)

It’s a bit unfortunate that the atomic mutation uses a different serialization format from Tuples, and perhaps there’s space for some kind of syntactic sugar in the Java API to do the conversion for you (for example, some kind of `void tr.add(byte[] key, long value)` and then I guess `long tr.getLong(byte[] key)`), but the sample code linked above uses a `ByteBuffer` to encode and decode in a compatible format.