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JVM Instructions 1

Many programs deal with character strings so here we give a brief introduction to the String class in the core Java language. Although strings in Java are class objects, in several ways they act like primitive types.

Note: You don't need to understand the concepts of classes and objects yet to use Java strings. In later chapters we discuss more details of the String class.

The String class makes creation and handling of strings quite easy and straightforward. While one could create arrays of char values, you will find it much simpler to use Java strings in most cases.

As with other classes, you can create an instance of a string with the new operator but to make life simpler, it is not required. So either of the following declarations will work:

    String str= new String("A string");

    String str1 = " and another string";

You can append one string to another with a simple "+" operation (which is the only case in Java of overloading an operator, that is, redefining its operation according to the type of operands). For example,

    String str2 = str + str1;

which results in str2 holding:

    "A string and another string";

A very useful capability of the "+" operator allows for default conversion of primitive type values to strings. Whenever you "add" a primitive type value, such as an int value, to a string, the primitive value converts to a String type and appends to the string. For example, this code

    String str1= "x = ";
    int i = 5;
    String str2 = str1 + 5;

results in str2 holding "x = 5". (This also works with boolean type values, resulting in the strings "true" and "false".)

The String class offers a large number of methods for accessing and manipulating the characters in the string, but we will discuss these futher in Chapter 10.

• String class in the Java API Specifications
• Java in a Nutshell, 4th Ed.

Latest update: Oct. 14, 2004

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