Exploring javalang in Java

Create QR Code ISO/IEC18004 in Java Exploring javalang

his chapter discusses thos e classes and interfaces defined by javalang As you know, javalang is automatically imported into all programs It contains classes and interfaces that are fundamental to virtually all of Java programming It is Java s most widely used package javalang includes the following classes:

Boolean Character ClassLoader Compiler Double Enum Float InheritableThreadLocal Integer Long Math Number Object Package Process ProcessBuilder Runtime RuntimePermission SecurityManager Short StackTraceElement StrictMath String StringBuffer StringBuilder System Thread ThreadGroup ThreadLocal Throwable Void

There are also two classes defined by the Character class: CharacterSubset and CharacterUnicodeBlock javalang defines the following interfaces:

Several of the classes contained in javalang contain deprecated methods, most dating back to Java 10 These deprecated methods are still provided by Java to support an evershrinking pool of legacy code and are not recommended for new code Most of the deprecations took place prior to Java SE 6, and these deprecated methods are not discussed here

Part II:

As mentioned in Part I of this book, Java uses primitive types, such as int and char, for performance reasons These data types are not part of the object hierarchy They are passed by value to methods and cannot be directly passed by reference Also, there is no way for two methods to refer to the same instance of an int At times, you will need to create an object representation for one of these primitive types For example, there are collection classes discussed in 17 that deal only with objects; to store a primitive type in one of these classes, you need to wrap the primitive type in a class To address this need, Java provides classes that correspond to each of the primitive types In essence, these classes encapsulate, or wrap, the primitive types within a class Thus, they are commonly referred to as type wrappers The type wrappers were introduced in 12 They are examined in detail here

The abstract class Number defines a superclass that is implemented by the classes that wrap the numeric types byte, short, int, long, float, and double Number has abstract methods that return the value of the object in each of the different number formats For example, doubleValue( ) returns the value as a double, floatValue( ) returns the value as a float, and so on These methods are shown here: byte byteValue( ) double doubleValue( ) float floatValue( ) int intValue( ) long longValue( ) short shortValue( ) The values returned by these methods can be rounded Number has six concrete subclasses that hold explicit values of each numeric type: Double, Float, Byte, Short, Integer, and Long

Double and Float are wrappers for floating-point values of type double and float, respectively The constructors for Float are shown here: Float(double num) Float(float num) Float(String str) throws NumberFormatException As you can see, Float objects can be constructed with values of type float or double They can also be constructed from the string representation of a floating-point number The constructors for Double are shown here: Double(double num) Double(String str) throws NumberFormatException Double objects can be constructed with a double value or a string containing a floatingpoint value

16:

The methods defined by Float are shown in Table 16-1 The methods defined by Double are shown in Table 16-2 Both Float and Double define the following constants:

MAX_EXPONENT MAX_VALUE MIN_EXPONENT MIN_NORMAL MIN_VALUE NaN POSITIVE_INFINITY NEGATIVE_INFINITY SIZE TYPE Maximum exponent (Added by Java SE 6) Maximum positive value Minimum exponent (Added by Java SE 6) Minimum positive normal value (Added by Java SE 6) Minimum positive value Not a number Positive infinity Negative infinity The bit width of the wrapped value The Class object for float or double

Method byte byteValue( ) static int compare(float num1, float num2)

Description Returns the value of the invoking object as a byte Compares the values of num1 and num2 Returns 0 if the values are equal Returns a negative value if num1 is less than num2 Returns a positive value if num1 is greater than num2 Compares the numerical value of the invoking object with that of f Returns 0 if the values are equal Returns a negative value if the invoking object has a lower value Returns a positive value if the invoking object has a greater value Returns the value of the invoking object as a double Returns true if the invoking Float object is equivalent to FloatObj Otherwise, it returns false Returns the IEEE-compatible, single-precision bit pattern that corresponds to num

int compareTo(Float f)

double doubleValue( ) boolean equals(Object FloatObj) static int floatToIntBits(float num)

static int floatToRawIntBits(float num) Returns the IEEE-compatible single-precision bit pattern that corresponds to num A NaN value is preserved float floatValue( ) int hashCode( ) static float intBitsToFloat(int num) int intValue( ) boolean isInfinite( ) static boolean isInfinite(float num) Returns the value of the invoking object as a float Returns the hash code for the invoking object Returns float equivalent of the IEEE-compatible, single-precision bit pattern specified by num Returns the value of the invoking object as an int Returns true if the invoking object contains an infinite value Otherwise, it returns false Returns true if num specifies an infinite value Other wise, it returns false

TABLE 16-1