Chapter 25

 

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25. The java.lang Package

The java.lang package contains the classes that are most central to the Java language. As you can see from Figure 25.1, the class hierarchy is broad rather than deep, which means that the classes are independent of each other.

Object is the ultimate superclass of all Java classes and is therefore at the top of all class hierarchies. Class is a class that describes a Java class. There is one Class object for each class that is loaded into Java.

Boolean, Character, Byte, Short, Integer, Long, Float, and Double are immutable class wrappers around each of the primitive Java data types. These classes are useful when you need to manipulate primitive types as objects. They also contain useful conversion and utility methods.

String and StringBuffer are objects that represent strings. String is an immutable type; StringBuffer may have its string changed in place.

Runtime provides a number of low-level methods associated with the Java run-time system. System provides similar low-level system methods. All the System methods are class methods, and this class may not be instantiated. Math is a similar class that supports only class methods--its methods provide floating-point math support.

The Thread class provides support for multiple threads of control running within the same Java interpreter. Process defines a platform-independent interface to platform-dependent processes running externally to the Java interpreter.

Throwable is the root class of the exception and error hierarchy. Throwable objects are used with the Java throw and catch statements. java.lang defines quite a few subclasses of Throwable. Exception and Error are the superclasses of all exceptions and errors. Figure 25.2 and Figure 25.3 show the class hierarchies for these core Java exceptions and errors.

public class AbstractMethodError extends IncompatibleClassChangeError {
    // Public Constructors
            public AbstractMethodError();
            public AbstractMethodError(String s);
}

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java.io.Writer (JDK 1.1)		java.lang.ArithmeticException (JDK 1.0)

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