Java test if is array

Java Program to Check if An Array Contains a Given Value

To understand this example, you should have the knowledge of the following Java programming topics:

Example 1: Check if Int Array contains a given value

class Main < public static void main(String[] args) < int[] num = ; int toFind = 3; boolean found = false; for (int n : num) < if (n == toFind) < found = true; break; >> if(found) System.out.println(toFind + " is found."); else System.out.println(toFind + " is not found."); > >

In the above program, we have an array of integers stored in variable num . Likewise, the number to be found is stored in toFind .

Now, we use a for-each loop to iterate through all elements of num and check individually if toFind is equal to n or not.

If yes, we set found to true and break from the loop. If not, we move to the next iteration.

Example 2: Check if an array contains the given value using Stream

import java.util.stream.IntStream; class Main < public static void main(String[] args) < int[] num = ; int toFind = 7; boolean found = IntStream.of(num).anyMatch(n -> n == toFind); if(found) System.out.println(toFind + " is found."); else System.out.println(toFind + " is not found."); > >

In the above program, instead of using a for-each loop, we convert the array to an IntStream and use its anyMatch() method.

anyMatch() method takes a predicate, an expression, or a function that returns a boolean value. In our case, the predicate compares each element n in the stream to toFind and returns true or false .

If any of the element n returns true , found is set to true as well.

Example 3: Check if an array contains a given value for non-primitive types

import java.util.Arrays; class Main < public static void main(String[] args)< String[] strings = ; String toFind= "Four"; boolean found = Arrays.stream(strings).anyMatch(t -> t.equals(toFind)); if(found) System.out.println(toFind + " is found."); else System.out.println(toFind + " is not found."); > >

In the above program, we’ve used a non-primitive data type String and used Arrays ‘s stream() method to first convert it to a stream and anyMatch() to check if the array contains the given value toFind .

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Determining If an Object Is an Array in Java

In order to determine if an object is an Object is an array in Java, we use the isArray() and getClass() methods.

The isArray() method checks whether the passed argument is an array. It returns a boolean value, either true or false

Syntax — The isArray() method has the following syntax —

The getClass() method method returns the runtime class of an object. The getClass() method is a part of the java.lang.Object class.

Declaration − The java.lang.Object.getClass() method is declared as follows −

public final Class getClass()

The getClass() method acts as the intermediate method which returns an runtime class of the object, which enables the terminal method, isArray() to verify it.

Example

Let us see a program to check if an object is an array or not −

public class Example < public static void main(String[] args) throws Exception < String str = "Hello"; String atr[][]= new String[10][20]; System.out.println("Checking for str. "); checkArray(str); System.out.println("Checking for atr. "); checkArray(atr); >public static void checkArray( Object abc) < boolean x = abc.getClass().isArray(); if(x == true) System.out.println("The Object is an Array"); else System.out.println("The Object is not an Array"); >>

Output

Checking for str. The Object is not an Array Checking for atr. The Object is an Array

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A Java instanceof array example

While working with “Java instanceof ” tests recently, my curiosity was piqued and I thought I’d take a look at how the instanceof operator works when testing against a Java array.

A Java ‘instanceof array’ example

To that end, I created the following Java instanceof array example class. To make my findings really stand out well, I ended up creating two different methods, instanceTester , and arrayTester , and call both of them with a simple Java String array:

/** * A Java ‘instanceof’ array example/test class. * @author alvin alexander, alvinalexander.com. */ public class JavaInstanceofArrayExample < public static void main(String[] args) < String[] array = ; instanceTester(array); arrayTester(array); > /** * A method that tests to see if the given object is * an instance of a String. */ static void instanceTester(Object object) < // see if the object is a String instance if (object instanceof String) System.out.println("object is a String"); else System.out.println("object is not a String"); >/** * A method that test to see if the given object is * an instance of a String array. */ static void arrayTester(Object[] objectArray) < // see if the object is a String array instance if (objectArray instanceof String[]) System.out.println("objectArray is a String array"); else System.out.println("objectArray is not a String array"); >>

(Before going on, it might be fun/helpful to make a note of what you think the output from this instanceof example will look like.)

Example program output

If you’ve used the Java instanceof operator to test against arrays before, you may have known that the program output would look like this:

object is not a String objectArray is a String array

As you can see from the code, this happens because this test returns false :

if (object instanceof String)

while this test returns true :

if (objectArray instanceof String[])

The crazy thing about this test is that, to the best of my knowledge, I’ve never tried passing an object array into a method that had a simple Object signature, as I did in this code when calling the instanceTester method. As I was working on this article, once I saw that I could do something like this, I decided that I better try both tests: one comparison of the String array against the instanceof String test, and a second comparison of the String array against the instanceof String[] test.

Related “Java instanceof” articles

Here are links to some of my other Java instanceof tutorials:

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Java python test if an array is empty

The Array Has Only Null Elements Java initializes all the arrays of non-primitive types with null values at the time of instantiating the array. Therefore, if you do not assign non-null elements to the array, it will continue to contain the null values for all elements.

Check if Array Is Empty in Java

In this post, we will see how to check if array is empty in java.

The arrays are a data structure that facilitates storing multiple instances of data together in contiguous memory locations.

This article discusses different cases when an array is considered to be empty in Java. It also discusses methods to check, for different cases, if array is empty in Java.

Check if the Array Is Empty in Java

There are three different cases when Java considers an array to be empty. These are given as follows.

• The array variable has the null reference.
• The array does not contain any element.
• The array has only null elements.

The Array Variable Has the Null Reference

In this case, an array variable actually stores a null reference, therefore, storing virtually nothing. This case can arise from two different possibilities as given below.

When the array is not instantiated, the array variable has a null reference making it an empty array. For example,

Let us see the code to check this condition for Java arrays.

The Array Does Not Contain Any Element

However, if you instantiate the array with the size of the array as zero, it will not store any elements, therefore, making it an empty array.

To check if the array is empty in this case,

• Check the length of the array using the ‘length’ variable.
• The Java array object has a variable named ‘length’ that stores the number of elements in the array.
• If the length is zero, the array is empty.

Let us see an example that implements the steps given above.

The Array Has Only Null Elements

Java initializes all the arrays of non-primitive types with null values at the time of instantiating the array. Therefore, if you do not assign non-null elements to the array, it will continue to contain the null values for all elements.

Alternatively, you can manually assign the null values to all of the array elements. In both cases, Java considers the array to be empty.

To check if the array is empty in this case,

• Initialize a boolean flag variable to true.
• Loop through all elements of the array.
• Check each element for a null value.
  • If the current element is not null, change the value of the flag variable to false and break from the loop.
  • Otherwise, move to the next element.
  • If the flag is true, the array is empty.
  • Otherwise, the array is not empty.

  Let us see the implementation of these steps in code.

  Note that the code declares a String array rather than an integer array as in previous cases. This is because the arrays with primitive data types are not initialized with null values by Java. For example, the integer array is initialized with zeros.

  On the other hand, String is a class in Java, therefore, the String array is initialized with null values.

  Further reading:

  Initialize empty array in java

  How to declare a String array in java

  Using the Java Library to Check if the Array Is Empty in Java

  Starting with the Java 8 version, Java provides library methods to perform a check on all array elements. Therefore, we can use these methods to check the condition of all null values in the array.

  The java.util.Arrays class defines the stream() method that can be used to call the allMatch() method.

  The stream() method returns a stream created using the array passed to it as a parameter. Let us see the definition of the stream() method.

  The allMatch() method accepts a predicate (a condition to be checked) and returns a boolean value. The allMatch() method returns a boolean true if the condition is met on all the array values. Otherwise, it returns a boolean false. Let us see the definition of the allMatch() method.

  Note that using this method you can only check the condition of the empty array where all elements of the array are null. Let us see the example in code.

  The code passes the isNull predicate condition of the Objects class to the allMatch() method. It means that the allMatch() method returns true if all the elements of the array have null values.

  Using Apache commons library to Check if the Array Is Empty in Java

  The Apache commons library provides the isEmpty() method in the ArrayUtils class. This method can be used to check if the array is empty in Java.
  You need to add below dependency to get Apache commons jar.

  Let us see the definition of the isEmpty() method.

  This method checks if the array passed to it as a parameter is empty or null. It returns a boolean true if an array is empty or null. Otherwise, it returns false.

  Let us see the example demonstrating its use in the code.

  You should note that this method only checks the following conditions.

  It can not check if the array has all null values.

  Conclusion

  While working with arrays, especially in the cases where arrays are passed as parameters to methods, you should perform the checks for an empty array. This helps in preventing the unexpected failures of the program.

  Apart from the direct methods, you can use the libraries to check the cases of the empty array in Java. However, you should be careful while using library methods. This is because, as we have discussed, both of the library methods work only for a subset of cases of an empty array.

  Hope you have enjoyed reading the article. Stay tuned for more such articles.

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  Java check if array has null elements Code Example, java check if array element is null ; 1. public class test < ; 2. ​ ; 3. public static void main(String[] args) < ; 4. Object[][] someArray = new

  Empty check with String[] array [duplicate]

  Normally you would want to do something like:

  if (arr != null && arr.length > 0)

  However, as you may suspect, someone have made utils for such kind of common action. For example, in Commons-lang, you can do something like:

  if you do a static import for ArrayUtils.isEmpty , this line can be even shorter and looks nicer:

  if(name!=null && name.length > 0) < // This means there are some elements inside name array. >else < // There are no elements inside it. >

  To check if a string array is empty.

  public boolean isEmptyStringArray(String [] array) < for(int i=0; i> return true; > 

  Check if an array is empty or not in JavaScript, The array can be checked if it is empty by using the array.length property. This property returns the number of elements in the array. If the

  Null Pointer Excpetion when trying to test if array is empty java

  If table is null . The act of performing table[index] dereferences the array, which causes a NullPointerException . A null array is not a empty array. A null array roughly corresponds to that fact that there is no array at all, and the table variable points to nothing.

  Please make the distinction between a null array, an empty array and a null element in a non-empty array.

  Element 0 in array is null:

  Similarly, you cannot call methods from a null object. If table[index] returns a null element, calling getKey() upon it could result in NullPointerException . Same goes if getKey() is null and then trying to call equals() on that.

  Please note an uninitialized array is implicitly null . Make sure you actually initialize the array.

  The NullPointer Exception could be because either:

  In case 1, the evaluation of the expression table[index] != null is a read of an item from the table array. This will throw a NullPointerException if table is null.

  In case 2, if table[index].getKey() returns null, then the expression table[index].getKey().equals(key) is calling a method (equals) on a null object reference which results in the exception.

  Your table isn’t initialised, declare as

  static HashEntry[] table = new HashEntry[TABLE_SIZE]; 

  Also, if HashEntry.getKey() can return null , make sure you check for this (or just flip the equals, i.e. !key.equals(table[index].getKey())

  C# — If (Array.Length == 0), You can use .Length == 0 if the length is empty and the array exists, but are you

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