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I got confused with the String concatenation.
String s1 = 20 + 30 + "abc" + (10 + 10);
String s2 = 20 + 30 + "abc" + 10 + 10;
System.out.println(s1);
System.out.println(s2);
The output is:
50abc20
50abc1010
I wonder why 20 + 30 are added together in both cases, but 10 + 10 require parenthese in order to be added (s1) instead of concatenated to the String (s2). Please explain how the String operator + works here.
314
Using the + operator is the most common way to concatenate two strings in Java. You can provide either a variable, a number, or a String literal (which is always surrounded by double quotes). Be sure to add a space so that when the combined string is printed, its words are separated properly.
Using + Operator It's very easy to use + operator for string concatenation. This operator can be used to add multiple strings together. However, the arguments must be a string. Note: Strings are immutable, therefore, whenever it is concatenated, it is assigned to a new variable.
In Java, two strings can be concatenated by using the + or += operator, or through the concat() method, defined in the java. lang. String class.
The same + operator you use for adding two numbers can be used to concatenate two strings. You can also use += , where a += b is a shorthand for a = a + b .
Addition is left associative. Taking the first case
20+30+"abc"+(10+10)
----- -------
50 +"abc"+ 20 <--- here both operands are integers with the + operator, which is addition
---------
"50abc" + 20 <--- + operator on integer and string results in concatenation
------------
"50abc20" <--- + operator on integer and string results in concatenation
In the second case:
20+30+"abc"+10+10
-----
50 +"abc"+10+10 <--- here both operands are integers with the + operator, which is addition
---------
"50abc" +10+10 <--- + operator on integer and string results in concatenation
----------
"50abc10" +10 <--- + operator on integer and string results in concatenation
------------
"50abc1010" <--- + operator on integer and string results in concatenation
Adding to the concept of associativity, you could ensure that two integers are never added together by using parentheses to always pair a string with an integer so the desired concatenation operation will take place rather than an addition.
String s4 = ((20 + (30 + "abc")) + 10)+10;
would produce:
2030abc1010
Also, to add to this topic, as the wrong part of the answer of Jonathan Schober tipped me off on a thing to keep in mind:
a+=something is not equal to a=a+<something> : the += evaluates the right side first, and only then adds it to the left side. So it has to be rewritten, it is equivalent to:
a=a+(something); //notice the parentheses!
Showing the difference
public class StringTest {
public static void main(String... args){
String a = "";
a+=10+10+10;
String b = ""+10+10+10;
System.out.println("First string, with += : " + a);
System.out.println("Second string, with simple =\"\" " + b);
}
}
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