Java String Array

Java String array is used to hold fixed number of Strings. String array is very common in simple java programs, specially among beginners to java and to test some specific scenarios. Even java main method argument is string array - public static void main(String[] args). So today we will look into different aspects of java string array with example programs.

• Java String array is basically an array of objects.
• There are two ways to declare string array - declaration without size and declare with size.
• There are two ways to initialize string array - at the time of declaration, populating values after declaration.
• We can do different kind of processing on string array such as iteration, sorting, searching etc.

Let’s go over java string array example programs now.

Java String Array Declaration

Below code snippet shows different ways for string array declaration in java.

String[] strArray; //declare without size

String[] strArray1 = new String[3]; //declare with size

Note that we can also write string array as String strArray[] but above shows way is the standard and recommended way. Also in the above code, strArray is null whereas strArray1 value is [null, null, null].

Java String Array Initialization

Let’s look at different ways to initialize string array in java.

//inline initialization
String[] strArray1 = new String[] {"A","B","C"};
String[] strArray2 = {"A","B","C"}; 

//initialization after declaration
String[] strArray3 = new String[3];
strArray3[0] = "A";
strArray3[1] = "B";
strArray3[2] = "C";

All the three string arrays will have same values. However if you will call equals method on them, it will return false.

System.out.println(strArray1.equals(strArray2)); // false
System.out.println(Arrays.toString(strArray1).equals(Arrays.toString(strArray2)));// true

The reason is that array are Objects and Object class implements equals() method like below.

public boolean equals(Object obj) {
        return (this == obj);
    }

Second statement is true because when converted to String, their values are same and String class equals() method implementation check for values. For more details, please check String class API documentation.

Iterating over java string array

We can iterate over string array using java for loop or java foreach loop.

String[] strArray2 = {"A","B","C"}; 
for (int i = 0; i < strArray2.length; i++) {
	System.out.print(strArray2[i]);
}

for (String str : strArray2) {
	System.out.print(str);
}

Search for a String in the String array

We can use for loop to search for an string in the array, below is a simple example for that.

package com.journaldev.stringarray;

public class JavaStringArrayExample {

	public static void main(String[] args) {
		String[] strArray = { "A", "B", "C" };
		
		boolean found = false;
		int index = 0;
		String s = "B";
		for (int i = 0; i < strArray.length; i++) {
			if(s.equals(strArray[i])) {
				index = i; found = true; break;
			}
		}
		if(found)
			System.out.println(s +" found at index "+index);
		else
			System.out.println(s +" not found in the array");
		
	}

}

Notice the use of break keyword to get out of the loop as soon as we found the string.

Java String Array Sorting

We can implement our own sorting algorithm, or we can use Arrays class sorting method.

String[] vowels = {"a","i","u","e","o"};
		
System.out.println("Before sorting "+Arrays.toString(vowels));

Arrays.sort(vowels);
		
System.out.println("After sorting "+Arrays.toString(vowels));

Output of above code snippet will be:

Before sorting [a, i, u, e, o]
After sorting [a, e, i, o, u]

Note that String implements Comparable interface, so it works for natural sorting. Incase you want to sort by some other way, you can use Arrays.sort() overloaded method by passing a Comparator. Learn about these sorting techniques at Comparable and Comparator in java.

Convert String to String Array

We can convert String to string array using it’s split() method. It’s useful when you get a single string as input with values separated using delimiter character.

String str = "a,e,i,o,u";
String[] vowels = str.split(",");
System.out.println(Arrays.toString(vowels)); //[a, e, i, o, u]

Convert String Array to String

We can use Arrays.toString() method to convert String array to String. Note that array doesn’t implement toString() method, so if you will try to get it’s string representation then you will have to rely on Arrays class, or else write your own custom code.

String[] vowels = { "a", "e", "i", "o", "u" };
System.out.println(vowels);
System.out.println(Arrays.toString(vowels));

Output will be like below.

[Ljava.lang.String;@3d04a311
[a, e, i, o, u]

The first output is because of Object class toString() implementation like below.

public String toString() {
        return getClass().getName() + "@" + Integer.toHexString(hashCode());
    }

Java String Array to List

We can get a list representation of string array using Arrays.toList() method. Note that this list is backed by the array and any structural modification will result in java.lang.UnsupportedOperationException.

String[] vowels = { "a", "e", "i", "o", "u", "a", "o" };

List<String> vowelsList = Arrays.asList(vowels);
System.out.println("vowelsList = "+vowelsList);
//vowelsList.add("x"); //java.lang.UnsupportedOperationException

vowelsList.set(0, "x"); //allowed because no structural modification
System.out.println("vowelsList = "+vowelsList);

That’s all for java string array. Reference: Arrays Oracle Documentation