Java Special String operations

1. String Literals

For each String literal in your program java automatically constructs String object. Thus, you can use a string literal to initialize a String object.

String s = “abc”;

Because a String object is created for every string literal, you can use a string literal at any place you can use a String object.

For example, you can call methods directly on a quoted string as it uses an object reference.

System.out.println(“abc”.length());

2. String Concatenation

In general, Java does not allow operators to be applied to String objects. The one exception to this rule is + operator, which concatenates two strings producing a String object as a result.

Example: The reference of the concatenated string “Rahul Jain Januthariya” will be stored in the reference variable name.

String name = “Rahul” + “ ”  +  “Jain”  +  “ ” + “Januthariya”

String Concatenation with other data types

If a string is concatenated with any data of type other than the string, the compiler converts the other operand (non-string) to its string equivalent.

Example:

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

Output: four:22

String Conversion and toString( )

When Java converts data into its String representation during concatenation, it does so by calling one of the overloaded versions of the String conversion method valueOf() defined by String class. The valueOf() is a static method overloaded for all simple types and for type Object.

For the simple types, valueOf() returns string that contains the human-readable equivalent of the value with which it is called. For objects, valueOf() calls the toString() method on the object.

Every class inherits toString(), because it is defined by the Object class. However, the default implementation of the toString() is seldom sufficient. It displays name of the class followed by symbol “@” and then object-id (e.g. Box@ab1232), which is normally of no use. For most important classes that you create, you will want to override toString() and provide your own string representations.

You can do so by overriding the toString( ) method:

String toString()

Example:

class Box

{ double w, h, d;

Box( double w, double h, double d)

{ this.w=w; this.h=h; this.d=d;

}

public String toString()

{ return "Dimensions are "+w+" by "+h+" by "+d+".";

}

class ToStringDemo1

{ public static void main(String args[])

{ Box b=new Box(10,12,14);

String s="Box b: "+b; //concates box object

System.out.println(b);

System.out.println(s);

}

}

Output:

Dimensions are 10.0 by 12.0 by 14.0.

Box b: Dimensions are 10.0 by 12.0 by 14.0

Note: If toString() is not overridden, the output of this program will be something like:

Box@b8df17

Box b: Box@b8df17