Try the [`Random.nextBytes`](http://download.oracle.com/javase/1.5.0/docs/api/java/util/Random.html#nextBytes(byte[])) method:

    byte[] b = new byte[20];
    new Random().nextBytes(b);


If you want a cryptographically strong random number generator (also thread safe) without using a third party API, you can use `SecureRandom`.

Java 6 &amp; 7:

    SecureRandom random = new SecureRandom();
    byte[] bytes = new byte[20];
    random.nextBytes(bytes);

Java 8 (even more secure):

    byte[] bytes = new byte[20];
    SecureRandom.getInstanceStrong().nextBytes(bytes);

If you are already using Apache Commons Lang, the  [`RandomUtils`](http://commons.apache.org/proper/commons-lang/javadocs/api-release/org/apache/commons/lang3/RandomUtils.html)  makes this a one-liner:

    byte[] randomBytes = RandomUtils.nextBytes(20);

Note: this does not produce cryptographically-secure bytes.

Java 7 introduced [ThreadLocalRandom](http://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ThreadLocalRandom.html) which is ***isolated to the current thread***.

This is an another rendition of [maerics&#39;s solution](https://stackoverflow.com/a/5683221/330457).

&lt;!-- language: java --&gt;

    final byte[] bytes = new byte[20];
    ThreadLocalRandom.current().nextBytes(bytes);

Create a **Random** object with a seed and get the array random by doing:

    public static final int ARRAY_LENGTH = 20;

    byte[] byteArray = new byte[ARRAY_LENGTH];
    new Random(System.currentTimeMillis()).nextBytes(byteArray);
    // get fisrt element
    System.out.println(&quot;Random byte: &quot; + byteArray[0]);

For those wanting a more secure way to create a random byte array, yes the most secure way is:
```
byte[] bytes = new byte[20];
SecureRandom.getInstanceStrong().nextBytes(bytes);
```
BUT your threads might block if there is not enough randomness available on the machine, depending on your OS. The following solution will not block:

```
SecureRandom random = new SecureRandom();
byte[] bytes = new byte[20];
random.nextBytes(bytes);
```

This is because the first example uses `/dev/random` and will block while waiting for more randomness (generated by a mouse/keyboard and other sources). The second example uses `/dev/urandom` which will not block.




I&#39;m getting image data (as `byte[]`) from DB. How to return this image in `@ResponseBody` ?

**EDIT**

I did it without `@ResponseBody` using `HttpServletResponse` as method parameter:

	@RequestMapping(&quot;/photo1&quot;)
	public void photo(HttpServletResponse response) throws IOException {
		response.setContentType(&quot;image/jpeg&quot;);
		InputStream in = servletContext.getResourceAsStream(&quot;/images/no_image.jpg&quot;);
		IOUtils.copy(in, response.getOutputStream());
	}
	

Using `@ResponseBody` with registered `org.springframework.http.converter.ByteArrayHttpMessageConverter` converter as @Sid said doesn&#39;t work for me :(.

	@ResponseBody
	@RequestMapping(&quot;/photo2&quot;)
	public byte[] testphoto() throws IOException {
		InputStream in = servletContext.getResourceAsStream(&quot;/images/no_image.jpg&quot;);
		return IOUtils.toByteArray(in);
	}



Spring MVC: How to return image in @ResponseBody?

I need to find out if a function exists in a database, so that I can drop it and create it again. It should basically be something like the following code that I use for stored procedures:


    IF EXISTS (
         SELECT  *
         FROM    dbo.sysobjects
         WHERE   id = OBJECT_ID(N&#39;[dbo].[SP_TEST]&#39;)
                 AND OBJECTPROPERTY(id, N&#39;IsProcedure&#39;) = 1 )


How to check if a function exists in a SQL database?

How can I create an array of 20 random bytes in Java?

How to create an array of 20 random bytes?

<p>How can I create an array of 20 random bytes in Java?</p>


I have two byte arrays and I am wondering how I would go about adding one to the other or combining them to form a new byte array. 






How to combine two byte arrays

I want to convert a `java.util.Date` object to a `String` in Java.

The format is `2010-05-30 22:15:52` 

Convert java.util.Date to String

I have a question about JUnit `assertEquals` to test `double` values. Reading the [API doc](https://junit.org/junit4/javadoc/latest/org/junit/Assert.html#assertEquals(double,%20double)) I can see:

&gt;     @Deprecated
&gt;     public static void assertEquals(double expected, double actual)
&gt;     
&gt; **Deprecated.** Use `assertEquals(double expected, double actual, double delta)` instead.

*(Note: in older documentation versions, the delta parameter is called epsilon)*

What does the `delta` (or `epsilon`) parameter mean?




Meaning of delta or epsilon argument of assertEquals for double values

How to convert a Java String to an ASCII byte array?


I understand that `HashSet` is based on `HashMap` implementation but is used when you need unique set of elements. So why in the next code when putting same objects into the map and set we have size of both collections equals to 1? Shouldn&#39;t map size be 2? Because if size of both collection is equal I don&#39;t  see any difference of using this two collections.

        Set testSet = new HashSet&lt;SimpleObject&gt;();
		Map testMap = new HashMap&lt;Integer, SimpleObject&gt;();	
		
		SimpleObject simpleObject1 = new SimpleObject(&quot;Igor&quot;, 1);
		SimpleObject simplObject2 = new SimpleObject(&quot;Igor&quot;, 1);
		testSet.add(simpleObject1);
		testSet.add(simplObject2);
		
		
		Integer key = new Integer(10);
		
		testMap.put(key, simpleObject1);
		testMap.put(key, simplObject2);
		
		System.out.println(testSet.size());
		System.out.println(testMap.size());

 The output is 1 and 1. 

    SimpleObject code

    public class SimpleObject {

	private String dataField1;
	private int dataField2;
	
	public SimpleObject(){}
	
	public SimpleObject(String data1, int data2){
		this.dataField1 = data1;
		this.dataField2 = data2;
	}
	
	public String getDataField1() {
		return dataField1;
	}

	public int getDataField2() {
		return dataField2;
	}

	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result
				+ ((dataField1 == null) ? 0 : dataField1.hashCode());
		result = prime * result + dataField2;
		return result;
	}

	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		SimpleObject other = (SimpleObject) obj;
		if (dataField1 == null) {
			if (other.dataField1 != null)
				return false;
		} else if (!dataField1.equals(other.dataField1))
			return false;
		if (dataField2 != other.dataField2)
			return false;
		return true;
	 }
    }


Java HashSet vs HashMap

I need to return multiple values from a function, therefore I have added them to an array and returned the array.

    &lt;?
    function data(){
        $a = &quot;abc&quot;;
        $b = &quot;def&quot;;
        $c = &quot;ghi&quot;;
    
        return array($a, $b, $c);
    }
    ?&gt;

How can I receive the values of `$a`, `$b`, `$c` by calling the above function?

How to access the elements of a function&#39;s return array?

How does passing a statically allocated array by reference work?

    void foo(int (&amp;myArray)[100])
    {
    }
    
    int main()
    {
        int a[100];
        foo(a);
    }

Does `(&amp;myArray)[100]` have any meaning or its just a syntax to pass any array by reference?
I don&#39;t understand separate parenthesis followed by big brackets here. Thanks.

Passing an array by reference

so when you initialize an array, you can assign multiple values to it in one spot:

    int array [] = {1,3,34,5,6}

but what if the array is already initialized and I want to completely replace the values of the elements in that array in one line

so 

    int array [] = {1,3,34,5,6}
    array [] = {34,2,4,5,6}

doesn&#39;t seem to work...

is there a way to do so?

c++ array assignment of multiple values

I always assumed caching the length of an array in JavaScript is a good idea (especially in the condition of a `for` loop) because of the expensiveness of calculating the length of an array.

### Example

    for (var i = 0; i &lt; arr.length; i++) { }
    
    // vs
    
    for (var i = 0, arrLength = arr.length; i &lt; arrLength; i++) { }


However, I thought perhaps the `length` property is only updated on creation and alteration of the array. Therefore, reading it shouldn&#39;t be too expensive an operation as opposed to reading it stored in a variable (as opposed to other methods in other languages that may need to seek in memory to find the end of something, e.g. `strlen()` in C).

I have two questions. I am also interested in how this works, so please don&#39;t hit me with the *premature optimisation* stick.

Assume the JavaScript engines in browsers.

1. Is there any advantage to caching the `length` property of an array in JavaScript? Is there much more involved in reading a local variable over an object&#39;s property?
2. Is the `length` property simply altered on creation and on `shift()` and `pop()` type methods that don&#39;t return a new array and otherwise simply stored as an integer?



Is reading the `length` property of an array really that expensive an operation in JavaScript?

How to use random in BATCH script?

I need to generate random color names e.g. &quot;Red&quot;, &quot;White&quot; etc. How can I do it? I am able to generate random color like this: 

    Random randonGen = new Random();
    Color randomColor = Color.FromArgb(randonGen.Next(255), randonGen.Next(255), 
    randonGen.Next(255));

but I need the names and not all colors generated like this have a known name.

Thanks

How to generate random color names in C#

Is it valid to share one instance of the `Random` class between multiple threads? And to call `nextInt(int)` from multiple threads in particular?

Is Random class thread safe?

I am waiting for another developer to finish a piece of code that will return an np array of shape (100,2000) with values of either -1,0, or 1.

In the meantime, I want to randomly create an array of the same characteristics so I can get a head start on my development and testing. The thing is that I want this randomly created array to be the same each time, so that I&#39;m not testing against an array that keeps changing its value each time I re-run my process.

I can create my array like this, but is there a way to create it so that it&#39;s the same each time. I can pickle the object and unpickle it, but wondering if there&#39;s another way.

    r = np.random.randint(3, size=(100, 2000)) - 1


Consistently create same random numpy array

How can I create an array with 40 elements, with random values from 0 to 39 ?
Like

    [4, 23, 7, 39, 19, 0, 9, 14, ...]

I tried using solutions from here:

http://freewebdesigntutorials.com/javaScriptTutorials/jsArrayObject/randomizeArrayElements.htm


but the array I get is very little randomized. It generates a lot of blocks of successive numbers...

Content Type	Original Author	Original Content on Stackoverflow
Question	novicePrgrmr	View Question on Stackoverflow
Solution 1 - Java	maerics	View Answer on Stackoverflow
Solution 2 - Java	DavidR	View Answer on Stackoverflow
Solution 3 - Java	Duncan Jones	View Answer on Stackoverflow
Solution 4 - Java	Jin Kwon	View Answer on Stackoverflow
Solution 5 - Java	ΦXocę 웃 Пepeúpa ツ	View Answer on Stackoverflow
Solution 6 - Java	Tom Hage	View Answer on Stackoverflow

How to create an array of 20 random bytes?

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How to check if a function exists in a SQL database?

Spring MVC: How to return image in @ResponseBody?

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