How do I convert a byte array with null terminating character to a String in Java?

Question

How can I create a String object from a byte array

byte arr[MAX_SIZE];  // Java

where one of the array elements is a C null terminating byte? Is it as simple as calling

String str = new String( arr );

Will the String constructor know to automatically stop at the null terminating character? Any bytes after the null byte are (possibly) garbage characters that I don't want to include in the string. The last response under Parsing byte array containg fields of unknown length suggests looping through the array and manually finding the null terminating character, but I was wondering whether the String constructor will do this automatically. I also assume the system's default charset will be used on all ends.

Stephen C · Accepted Answer · 2021-08-30 22:59:37Z

byte arr[] = ...
Charset charset = ...

// Find the position of the first zero byte
int i;
for (i = 0; i < arr.length && arr[i] != 0; i++) { }


String str = new String(arr, 0, i, charSet);

Notes:

It is generally a good idea to use an explicit CharSet parameter so that your application doesn't depend on the platform's default characterset / encoding.
This won't work for some charsets. For instance, a UTF-16 encoded string can't safely be represented as a zero-terminated byte sequence because many code units contain zero bytes. (On the other hand, UTF-8 is OK provided that the string contains no instances of code point zero; see Can UTF-8 contain zero byte?)

... but I was wondering whether the String constructor will do this automatically.

No it / they won't. (Don't "wonder" ... read the javadoc :-))

I also assume the system's default charset will be used on all ends.

If you don't specify a charset, the Java platform's default will be used. This is likely to be the system default, but that is not guaranteed.

Eric · Accepted Answer · 2015-11-20 15:35:20Z

14

try this: String s = new String(arr).trim()

answered Nov 20, 2015 at 15:35

Eric

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3 Comments

Peter Over a year ago

trim() removes the null character at the end of my strings just fine...

Sanjeev Over a year ago

trim() will only work if all characters at the end of the array are zero (e.g [65, 66, 67, 0, 0, 0]: this converts to "ABC") but not with junk characters after the terminator (e.g. [65, 66 ,67, 0, -12, 10 , 33]).

astroboy Over a year ago

For any Kotlin dev that might stumble upon this: the trim() works only for java.lang.String, it doesn't work for regular Kotlin strings.

davogotland · Accepted Answer · 2012-01-12 22:30:40Z

12

how about this:

String str = new String(arr).split("\0")[0];

answered Jan 12, 2012 at 22:30

davogotland

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2 Comments

sjr Over a year ago

Doesn't look too good if the input array is huge, unless you are going to read all the strings anyway.

Stephen C Over a year ago

This is making assumptions about the default charset. And it is creating a large temporary string, an array an potentially a large number of unnecessary strings for the stuff after the first null.

sjr · Accepted Answer · 2012-01-12 22:24:51Z

4

It won't magically stop at the null terminator. The null character doesn't terminate strings in Java. You will have to find the index of the first null character and stop there. Use the String(byte[] arr, int offset, length) constructor after that.

answered Jan 12, 2012 at 22:24

sjr

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2 Comments

Phillip Over a year ago

The NULL char is not necessarily toward the end of the array; it can be at any position.

sjr Over a year ago

@Phillip, realised this after reading your question again.. edited my answer

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