Two Meanings of Plus In Java the symbol can be used to add

Two Meanings of Plus

In Java, the symbol + can be used to add numbers or to concatenate strings. This exercise illustrates both uses.When using a string literal (a sequence of characters enclosed in double quotation marks) in Java the complete string must fit on one line. The following is NOT legal (it would result in a compile-time error). System.out.println (\"It is NOT okay to go to the next line in a LONG string!!!\");

The solution is to break the long string up into two shorter strings that are joined using the concatenation operator (which is the + symbol). This is discussed in Section 2. 1 in the text. So the following would be legal System.out.println (\"It is OKAY to break a long string into \" + \"parts and join them with a + symbol.\"); So, when working with strings the + symbol means to concatenate the strings (join them). BUT, when working with numbers the + means what it has always meant—add!

1.

Observing the Behavior of

+ To see the behavior of + in different settings do the following:

a. Study the program below, which is in file

PlusTest.java.

// ************************************************************

//

PlusTest.java

//

// Demonstrate the different behaviors of the + operator

// ************************************************************

public class PlusTest

{

// -------------------------------------------------

// main prints some expressions using the + operator

// -------------------------------------------------

public static void main (String[] args)

{

System.out.println (\"This is a long string that is the \" + \"concatenation of two shorter strings.\");

System.out.println (\"The first computer was invented about\" + 55 + \"years ago.\");

System.out.println (\"8 plus 5 is \" + 8 + 5);

System.out.println (\"8 plus 5 is \" + (8 + 5)) ;

System.out.println (8 + 5 + \" equals 8 plus 5.\");

}

}

b. Save PlusTest.java to your directory.

c. Compile and run the program. For each of the last three output statements (the ones dealing with 8 plus 5) write down what was printed. Now for each explain why the computer printed what it did given that the following rules are used for +. Write out complete explanations.

Solution

The output is :

This is a long string that is the concatenation of two shorter strings

The first computer was invented about55years ago

8 plus 5 is85

8 plus 5 is 13

85equals 8 plus 5

In the first output line + acts as a concatenation operator

In 2nd line also as concatenatiion operator

In 3rd line also as concatenation operator for 3 operands

In 4th line + inside brackets act as addition operator evaluates as expression and outside one acts as concatenation

In 5th line + acts as concatenation only.