String Concatenation using Java

By: Syed Fazal Emailed: 1749 times Printed: 2436 times    

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In general, Java does not allow operators to be applied to String objects. The one exception to this rule is the + operator, which concatenates two strings, producing a String object as the result. This allows you to chain together a series of + operations. For example, the following fragment concatenates three strings:

String age = "9";
String s = "He is " + age + " years old.";
System.out.println(s);

This displays the string "He is 9 years old."

One practical use of string concatenation is found when you are creating very long strings. Instead of letting long strings wrap around within your source code, you can break them into smaller pieces, using the + to concatenate them. 

Here is an example:
// Using concatenation to prevent long lines.
class ConCat {
public static void main(String args[]) {

String longStr = "This could have been " +
"a very long line that would have " +
"wrapped around. But string concatenation " +
"prevents this.";
System.out.println(longStr);

        }
}

String Concatenation with other Data Types

You can concatenate strings with other types of data. For example, consider this slightly different version of the earlier example:

int age = 9;
String s = "He is " + age + " years old.";
System.out.println(s);

In this case, age is an int rather than another String, but the output produced is the same as before. This is because the int value in age is automatically converted into its string representation within a String object. This string is then concatenated as before. The compiler will convert an operand to its string equivalent whenever the other operand
of the + is an instance of String. Be careful when you mix other types of operations with string concatenation expressions, however. You might get surprising results. Consider the following:

String s = "four: " + 2 + 2;
System.out.println(s);

This fragment displays
four: 22


rather than the


four: 4

that you probably expected. Here's why. Operator precedence causes the concatenation of "four" with the string equivalent of 2 to take place first. This result is then concatenated with the string equivalent of 2 a second time. To complete the integer addition first, you must use parentheses, like this:

String s = "four: " + (2 + 2);
Now s contains the string "four: 4".


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Comments(8)


1. View Comment

but how is the string concatenation done with the '+' as java does not support operator overloading.

View Tutorial          By: Vipin at 2009-05-09 03:08:51
2. View Comment

string is immutable in java.String buffer is mutable.
so even though we add the symbol '+' for concatenation.
the string which supplied for concatenation is taken as a object of string buffer.
after the string buffer completes the necessary concatenation then its return the string by toString()


View Tutorial          By: krishnakumar at 2009-10-19 00:35:44
3. View Comment

@Vipin : vipin u r wrong,,,in reality java does not support explicitely perator verloading,,,,that is the rule,
java itself implicitely has done it,,,so we r not in the need of doing it explicitely,,,,java help us here,,,


View Tutorial          By: Arpit Tyagi at 2010-07-23 04:11:20
4. View Comment

..how if the input is THE DOG BARKS then the output will be "THE" "DOG" "BARKS" and it canbe rumbled..who can give me an example of that??
plz lang poh..
i needie now


View Tutorial          By: dharel at 2011-01-28 02:53:19
5. View Comment

guys you both are correct
but,java is implicit as wel as explicit
so,we can use '+' operator their to concat more than two strings;
if we want to concat two simply we can use concat operation"Ex:str1.concat(str2) if str1 and str2 are two strings"
finally, using '+' operator only we can concat three or more strings.......... is iam right kada.
if any other way is their plz mention


View Tutorial          By: vijay at 2011-09-08 12:12:48
6. View Comment

what about strings in J2ME ?

View Tutorial          By: Swapnil at 2012-07-20 09:19:15
7. View Comment

thaks sir for giving information about adding int + string

View Tutorial          By: vijay kumar at 2012-10-10 04:59:05
8. View Comment

how to pass user input string (like a user entered: user_query="USA"). this user_query will b sent to google page for search.
my Question is how i can concatenate user_query to a web page can any body help me????


View Tutorial          By: saif at 2012-12-04 19:51:26

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