concat() vs “+” operator : In Java for String concatenation

0 votes

Assuming String a and b:

a += b
a = a.concat(b)

Under the hood, are they the same thing?

Here is concat decompiled as reference. I'd like to be able to decompile the + operator as well to see what that does.

public String concat(String s) {

    int i = s.length();
    if (i == 0) {
        return this;
    }
    else {
        char ac[] = new char[count + i];
        getChars(0, count, ac, 0);
        s.getChars(0, i, ac, count);
        return new String(0, count + i, ac);
    }
}
Apr 27, 2018 in Java by developer_1
• 3,280 points
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Basically, there are two important differences between + and the concat method.

  1. If you are using the concat method then you would only be able to concatenate strings while in case of the + operator, you can also concatenate the string with any data type.

    For Example:

    String s = 10 + "Hello";

    In this case, the output should be 10Hello.

    String s = "I";
    String s1 = s.concat("am").concat("good").concat("boy");
    System.out.println(s1);

    In the above case you have to provide two strings mandatory.

  2. The second and main difference between + and concat is that:

    Case 1: Suppose I concat the same strings with concat operator in this way

    String s="I";
    String s1=s.concat("am").concat("good").concat("boy");
    System.out.println(s1);

    In this case total number of objects created in the pool are 7 like this:

    I
    am
    good
    boy
    Iam
    Iamgood
    Iamgoodboy

    Case 2:

    Now I am going to concatinate the same strings via + operator

    String s="I"+"am"+"good"+"boy";
    System.out.println(s);

    In the above case total number of objects created are only 5.

    Actually when we concatinate the strings via + operator then it maintains a StringBuffer class to perform the same task as follows:-

    StringBuffer sb = new StringBuffer("I");
    sb.append("am");
    sb.append("good");
    sb.append("boy");
    System.out.println(sb);

    In this way it will create only five objects.

So guys these are the basic differences between + and the concat method. Enjoy :)

answered Apr 27, 2018 by Rishabh
• 3,520 points

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