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It is important to note that the following statement does not modify the original object pointed to by the reference variable named str1 .
thisObj.str1 = thisObj.str1 + " " + thisObj.str2; Rather, this statement creates a new object, which is concatenation of two existing objects and causes the reference variable named str1 to point to the new object instead of the original object.
The original object then becomes eligible for garbage collection (unless there is another reference to the object hanging around somewhere) .
Many aspects of string manipulation can be accomplished in this manner, particularly when the methods of the String class are brought into play.
According to The Java Tutorial by Campione and Walrath:
"Because they are constants, Strings are typically cheaper than StringBuffers and they can be shared. So it's important to use Stringswhen they're appropriate."
The String and StringBuffer classes have numerous overloaded constructors and many different methods. I will attempt to provide asampling of constructors and methods that will prepare you to explore other constructors and methods on your own.
The next sample program touches on some of the possibilities provided by the wealth of constructors and methods in the String and StringBuffer classes.
At this point, I will refer you to Java OOP: Java Documentation where you will find a link to online Java documentation. Among other things, the online documentation provides a list of theoverloaded constructors and methods for the String and StringBuffer classes.
As of Java version 7, there are four overloaded constructors in the StringBuffer class and about thirteen different overloaded versions of the append method. There are many additional methods in the StringBuffer class including about twelve overloaded versions of the insert method.
As you can see, there are lots of constructors and lots of methods from which to choose. One of your challenges as a Java programmer will be to find the rightmethods of the right classes to accomplish what you want your program to accomplish.
The sample program shown in Listing 2 illustrates a variety of ways to create and initialize String and StringBuffer objects.
| Listing 2 . File String02.java. |
|---|
/*File String02.java Copyright 1997, R.G.Baldwin
Illustrates different ways to create String objects andStringBuffer objects.
The program was tested using JDK 1.1.3 under Win95.The output from this program is as follows. In some cases,
manual line breaks were inserted to make the material finthis presentation format.
Create a String the long way and display itString named str2
Create a String the short way and display itString named str1
Create, initialize, and display a StringBuffer using newStringBuffer named str3
Try to create/initialize StringBuffer withoutusing new - not allowedCreate an empty StringBuffer of default length
Now put some data in it and display itStringBuffer named str5
Create an empty StringBuffer and specify lengthwhen it is created
Now put some data in it and display itStringBuffer named str6
Try to create and append to StringBuffer withoutusing new -- not allowed
**********************************************************/class String02{
void d(String displayString){//method to display stringsSystem.out.println(displayString);
}//end method d()public static void main(String[] args){String02 o = new String02();//obj of controlling classo.d("Create a String the long way and display it");
String str1 = new String("String named str2");o.d(str1 + "\n");o.d("Create a String the short way and display it");
String str2 = "String named str1";o.d(str2 + "\n");o.d("Create, initialize, and display a StringBuffer " +
"using new");StringBuffer str3 = new StringBuffer(
"StringBuffer named str3");o.d(str3.toString()+"\n");
o.d("Try to create/initialize StringBuffer without " +"using new - not allowed\n");
//StringBuffer str4 = "StringBuffer named str4";xo.d("Create an empty StringBuffer of default length");StringBuffer str5 = new StringBuffer();o.d("Now put some data in it and display it");
//modify length as neededstr5.append("StringBuffer named str5");
o.d(str5.toString() + "\n");o.d("Create an empty StringBuffer and specify " +"length when it is created");
StringBuffer str6 = new StringBuffer("StringBuffer named str6".length());
o.d("Now put some data in it and display it");str6.append("StringBuffer named str6");
o.d(str6.toString() + "\n");o.d("Try to create and append to StringBuffer " +"without using new -- not allowed");
//StringBuffer str7;//str7.append("StringBuffer named str7");
}//end main()}//end class String02 |
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