Understanding the Concatenation of Strings in Java

Concatenation in the Java programming language is the operation of joining two strings together. You can join strings using either the addition () operator or the String’s concat() method. Using the Operator 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). To combine the strings â€Å"I’m a† and â€Å"student†, for example, write: I’m a student Be sure to add a space so that when the combined string is printed, its words are separated properly. Note above that student starts with a space, for example. Combining Multiple Strings Any number of operands can be strung together, for instance: I’m a student ! And so are you. Using the Operator in a Print Statement Frequently, the operator is used in a print statement. You might write something like: System.out.println(pan handle); This would print: panhandle Combining Strings Across Multiple Lines Java disallows literal strings to span more than a line. Using the operator prevents this: String quote Nothing in all the world is more dangerous than sincere ignorance and conscientious stupidity.;   Combining a Mixture of Objects The  operator   normally acts as an  arithmetic operator  unless one of its  operands  is a String. If so, it converts the other operand to a String before joining the second operand to the end of the first operand. For example, in the example below, age is an integer, so the operator will first convert it to a String and then combine the two strings. (The operator does this behind the scenes by calling its toString() method; you won’t see this occur.) int age 12;System.out.println(My age is age); This would print: My age is 12 Using the Concat Method The String class has a method concat() that performs the same operation. This method acts on the first string and then takes the string to combine as a parameter: public String concat (String str)​   For example: String myString I have decided to stick with love.;myString myString.concat( Hate is too great a burden to bear.);System.out.println(myString); This would print: I have decided to stick with love. Hate is too great a burden to bear. Differences Between the Operator and the Concat Method You may be wondering when it makes sense to use the operator to concatenate, and when you should use the concat() method.  Here are some differences between the two: The concat() method can combine only String objects — it must be called on a String object, and its parameter must be a String object. This makes it more restrictive than the operator since the operator silently converts any non-string argument to a string.The concat() method throws a NullPointerException if the object has a null reference, while the operator deals with a null reference as a â€Å"null† string.The concat()) method is capable of combining only two strings – it cannot take multiple arguments. The operator can combine any number of strings. For these reasons, the operator is more often used to combine strings. If you are developing a large-scale application, however, performance can differ between the two because of the way that Java handles string conversion, so be aware of the context in which you are combining strings.