visual basic barcode printing The Wrapper Constructors in Java

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The Wrapper Constructors
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All of the wrapper classes except Character provide two constructors: one that takes a primitive of the type being constructed, and one that takes a String representation of the type being constructed for example,
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Integer i1 = new Integer(42); Integer i2 = new Integer("42");
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Float f1 = new Float(3.14f); Float f2 = new Float("3.14f");
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TABLE 6-2
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Primitive boolean byte char double float int long short
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Wrapper Class Boolean Byte Character Double Float Integer Long Short
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Constructor Arguments boolean or String byte or String char double or String float or String int or String long or String short or String
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Wrapper Classes and Their Constructor Arguments
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6: Java.lang The Math Class, Strings, and Wrappers
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The Character class provides only one constructor, which takes a char as an argument for example,
Character c1 = new Character('c');
The constructors for the Boolean wrapper take either a boolean value true or false, or a case-insensitive String with the value true or false . But a Boolean object can t be used as an expression in a boolean test for instance,
Boolean b = new Boolean("false"); if (b) // won't compile, expecting a boolean not a Boolean
The valueOf() Methods
The static valueOf() methods provided in most of the wrapper classes give you another approach to creating wrapper objects. Both methods take a String representation of the appropriate type of primitive as their first argument, the second method (when provided) takes an additional argument, int radix, which indicates in what base (for example binary, octal, or hexadecimal) the first argument is represented for example,
Integer i2 = Integer.valueOf("101011", 2); // converts 101011 to 43 and // assigns the value 43 to the // Integer object i2
Float f2 = Float.valueOf("3.14f"); // assigns 3.14 to the Float object f2
Using Wrapper Conversion Utilities
As we said earlier, a wrapper s second big function is converting stuff. The following methods are the most commonly used, and are the ones you re most likely to see on the test.
xxxValue()
When you need to convert the value of a wrapped numeric to a primitive, use one of the many xxxValue() methods. All of the methods in this family are no-arg methods. As you can see by referring to Table 6-3, there are 36 xxxValue() methods. Each of the six numeric wrapper classes has six methods, so that any numeric wrapper can be converted to any primitive numeric type for example,
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Integer i2 = new Integer(42); byte b = i2.byteValue(); short s = i2.shortValue(); double d = i2.doubleValue();
// // // // // // //
make a new wrapper object convert i2's value to a byte primitive another of Integer's xxxValue methods yet another of Integer's xxxValue methods
Float f2 = new Float(3.14f); short s = f2.shortValue(); System.out.println(s); // // // // // make a new wrapper object convert f2's value to a short primitive result is 3 (truncated, not rounded)
TABLE 6-3
Common Wrapper Conversion Methods
Method s = static n = NFE exception
Boolean
Byte
Character
Double
Float
Integer
Long
Short
byteValue doubleValue floatValue intValue longValue shortValue parseXxx s,n
x x x x x x x x
x x x x x x x
x x x x x x x
x x x x x x x x
x x x x x x x x
x x x x x x x x
parseXxx s,n (with radix) valueOf s,n x
valueOf s,n (with radix)
6: Java.lang The Math Class, Strings, and Wrappers
TABLE 6-3
Common Wrapper Conversion Methods (continued)
Method s = static n = NFE exception
Boolean
Byte
Character
Double
Float
Integer
Long
Short
toString toString s (primitive) toString s (primitive, radix) toBinaryString s toHexString toOctalString s s
x x x
x x x
x x x
x x x
In summary, the essential method signatures for Wrapper conversion methods are primitive xxxValue( ) primitive parseXxx(String) Wrapper valueOf(String)
parseXxx() and valueOf()
The six parseXxx() methods (one for each numeric wrapper type) are closely related to the valueOf() method that exists in all of the numeric wrapper classes (plus Boolean). Both parseXxx() and valueOf() take a String as an argument, throw a NumberFormatException if the String argument is not properly formed, and can convert String objects from different bases (radix), when the underlying primitive type is any of the four integer types. (See Table 6-3.) The difference between the two methods is
parseXxx() returns the named primitive. valueOf() returns a newly created wrapped object of the type that invoked
the method. Some examples of these methods in action:
double d4 = Double.parseDouble("3.14"); System.out.println("d4 = " + d4); // convert a String to a primitive // result is "d4 = 3.14"
Double d5 = Double.valueOf("3.14"); // create a Double object System.out.println(d5 instanceof Double ); // result is "true"
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The next examples involve using the radix argument, (in this case binary):
long L2 = Long.parseLong("101010", 2); System.out.println("L2 = " + L2); Long L3 = Long.valueOf("101010", 2); System.out.println("L3 value = " + L3); // binary String to a primitive // result is "L2 = 42" // binary String to Long object // result is "L2 value = 42"
toString()
The class Object, the alpha class, the top dog, has a toString() method. Since we know that all other Java classes inherit from class Object, we also know (stay with me here) that all other Java classes have a toString() method. The idea of the toString() method is to allow you to get some meaningful representation of a given object. For instance, if you have a Collection of various types of objects, you can loop through the Collection and print out some sort of meaningful representation of each object using the toString() method, which is guaranteed to be in every class. We ll talk more about the toString() method in the Collections chapter, but for now let s focus on how the toString() method relates to the wrapper classes which, as we know, are marked final. All of the wrapper classes have a no-arg, nonstatic, instance version of toString(). This method returns a String with the value of the primitive wrapped in the object for instance,
Double d = new Double("3.14"); System.out.println("d = " + d.toString() ); // result is "d = 3.14"
All of the numeric wrapper classes provide an overloaded, static toString() method that takes a primitive numeric of the appropriate type (Double.toString() takes a double, Long.toString() takes a long, etc.), and, of course, returns a String with that primitive s value for example,
System.out.println("d = " + Double.toString(3.14); // result is "d = 3.14"
Finally, Integer and Long provide a third toString() method. It is static, its first argument is the appropriate primitive, and its second argument is a radix. The radix argument tells the method to take the first argument (which is radix 10 or base 10 by default), and convert it to the radix provided, then return the result as a String for instance,
System.out.println("hex = " + Long.toString(254,16); // result is "hex = fe"
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