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Java Fundamental Classes Reference

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12. The java.lang Package

The package java.lang contains classes and interfaces that are essential to the Java language. These include:

  • Object, the ultimate superclass of all classes in Java.

  • Thread, the class that controls each thread in a multithreaded program.

  • Throwable, the superclass of all error and exception classes in Java.

  • Classes that encapsulate the primitive data types in Java.

  • Classes for accessing system resources and other low-level entities.

  • Math, a class that provides standard mathematical methods.

  • String, the class that represents strings.

Because the classes in the java.lang package are so essential, the java.lang package is implicitly imported by every Java source file. In other words, you can refer to all of the classes and interfaces in java.lang using their simple names.

Figure 12.1 shows the class hierarchy for the java.lang package.

The possible exceptions in a Java program are organized in a hierarchy of exception classes. The Throwable class is at the root of the exception hierarchy. Throwable has two immediate subclasses: Exception and Error. Figure 12.2 shows the standard exception classes defined in the java.lang package, while Figure 12.3 shows the standard error classes defined in java.lang.

AbstractMethodError

Name

AbstractMethodError

Synopsis

Class Name:

java.lang.AbstractMethodError

Superclass:

java.lang.IncompatibleClassChangeError

Immediate Subclasses:

None

Interfaces Implemented:

None

Availability:

JDK 1.0 or later

Description

An AbstractMethodError is thrown when there is an attempt to invoke an abstract method.

Class Summary

public class java.lang.AbstractMethodError
             extends java.lang.IncompatibleClassChangeError {
  // Constructors
  public AbstractMethodError();
  public AbstractMethodError(String s);
}

Constructors

AbstractMethodError

public AbstractMethodError()

Description

This constructor creates an AbstractMethodError with no associated detail message.

public AbstractMethodError(String s)

Parameters

s

The detail message.

Description

This constructor creates an AbstractMethodError with the specified detail message.

Inherited Methods

Method

Inherited From

Method

Inherited From

clone()

Object

equals(Object)

Object

fillInStackTrace()

Throwable

finalize()

Object

getClass()

Object

getLocalizedMessage()

Throwable

getMessage()

Throwable

hashCode()

Object

notify()

Object

notifyAll()

Object

printStackTrace()

Throwable

printStackTrace(PrintStream)

Throwable

printStackTrace(PrintWriter)

Throwable

toString()

Object

wait()

Object

wait(long)

Object

wait(long, int)

Object

   

See Also

Error, IncompatibleClassChangeError, Throwable


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