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The values true and false are not keywords.
No. An object cannot be cast to a primitive value.
Yes, a double value can be cast to a byte.
Yes, a for statement can loop indefinitely. For example, consider the following: for(;;) ;
Yes, a lock can be acquired on a class. This lock is acquired on the class's Class object..
An abstract class may not be declared as final.
An anonymous class may implement an interface or extend a superclass, but may not be declared to do both.
Yes, an exception can be rethrown.
A reachable object cannot be garbage collected. Only unreachable objects may be garbage collected..
An object's finalize() method cannot be invoked by the garbage collector while the object is still reachable. However, an object's finalize() method may be invoked by other objects.
An unreachable object may become reachable again. This can happen when the object's finalize() method is invoked and the object performs an operation which causes it to become accessible to reachable objects.
Try statements may be tested.
A class does not inherit constructors from any of its superclasses.
Garbage collection does not guarantee that a program will not run out of memory. It is possible for programs to use up memory resources faster than they are garbage collected. It is also possible for programs to create objects that are not subject to garbage collection.
The only statements for which it makes sense to use a label are those statements that can enclose a break or continue statement.
Commas are used to separate multiple statements within the initialization and iteration parts of a for statement.
A Java source code file takes the name of a public class or interface that is defined within the file. A source code file may contain at most one public class or interface. If a public class or interface is defined within a source code file, then the source code file must take the name of the public class or interface. If no public class or interface is defined within a source code file, then the file must take on a name that is different than its classes and interfaces. Source code files use the .java extension.
Objects that subclass the Observable class maintain a list of observers. When an Observable object is updated it invokes the update() method of each of its observers to notify the observers that it has changed state. The Observer interface is implemented by objects that observe Observable objects.
The elements of a BorderLayout are organized at the borders (North, South, East, and West) and the center of a container.
The elements of a CardLayout are stacked, one on top of the other, like a deck of cards.
The elements of a GridBagLayout are organized according to a grid. However, the elements are of different sizes and may occupy more than one row or column of the grid. In addition, the rows and columns may have different sizes.
this is used to refer to the current object instance. super is used to refer to the variables and methods of the superclass of the current object instance.
A dead thread cannot be restarted.
A component can handle its own events by implementing the required event-listener interface and adding itself as its own event listener.
By associating Checkbox objects with a CheckboxGroup.
When an exception is thrown within the body of a try statement, the catch clauses of the try statement are examined in the order in which they appear. The first catch clause that is capable of handling the exception is executed. The remaining catch clauses are ignored.
It uses those low order bytes of the result that can fit into the size of the type allowed by the operation.
The operating system's task scheduler allocates execution time to multiple tasks. By quickly switching between executing tasks, it creates the impression that tasks execute sequentially.
The == operator compares two objects to determine if they are the same object in memory. It is possible for two String objects to have the same value, but located indifferent areas of memory.
The fractional part of the result is truncated. This is known as rounding toward zero.
An object's finalize() method may only be invoked once by the garbage collector.
A class that is declared without any access modifiers is said to have package access. This means that the class can only be accessed by other classes and interfaces that are defined within the same package.
A protected method may only be accessed by classes or interfaces of the same package or by subclasses of the class in which it is declared.
A private variable may only be accessed within the class in which it is declared.
Once an object is garbage collected, it ceases to exist. It can no longer become reachable again.
The String literal "abc" is not a primitive value. It is a String object.
No. It is not a valid java operator.
A class is a subclass of itself.
The null is not a keyword.
The sizeof operator is not a keyword.
It is written x ? y : z.
Window, Frame, Dialog, FileDialog, Panel, Applet, or ScrollPane.
The eight primitive types are byte, char, short, int, long, float, double, and boolean.
The Canvas, Frame, Panel, and Applet classes support painting.
Box.Filler, Button, Canvas, Checkbox, Choice, Container, Label, List, Scrollbar, or TextComponent.
TextField and TextArea.
The default value of the boolean type is false.
The default value of an String type is null.
The garbage collector invokes an object's finalize() method when it detects that the object has become unreachable.
An I/O filter is an object that reads from one stream and writes to another, usually altering the data in some way as it is passed from one stream to another.
E is the base of the natural logarithm and PI is mathematical value pi.
Order of precedence determines the order in which operators are evaluated in expressions. Associatity determines whether an expression is evaluated left-to-right or right-to-left.
Synchronized methods are methods that are used to control access to an object. A thread only executes a synchronized method after it has acquired the lock for the method's object or class. Synchronized statements are similar to synchronized methods. A synchronized statement can only be executed after a thread has acquired the lock for the object or class referenced in the synchronized statement.
The high-level thread states are ready, running, waiting, and dead.
The left operand is an object reference or null value and the right operand is a class, interface, or array type.
The Object class is the highest-level class in the Java class hierarchy. The Class class is used to represent the classes and interfaces that are loaded by a Java program..
Without layout managers, Java programmers are faced with determining how their GUI will be displayed across multiple windowing systems and finding a common sizing and positioning that will work within the constraints imposed by each windowing system.
A thread class may be declared as a subclass of Thread, or it may implement the Runnable interface.
A thread can enter the waiting state by invoking its sleep() method, by blocking on I/O, by unsuccessfully attempting to acquire an object's lock, or by invoking an object's wait() method. It can also enter the waiting state by invoking its (deprecated) suspend() method.
Wrapped classes are classes that allow primitive types to be accessed as objects.
The ObjectInputStream class supports the reading of objects from input streams.
The java.awt.AWTEvent class is the highest-level class in the AWT event-class hierarchy.
The Java runtime system generates RuntimeException and Error exceptions.
A catch clause can catch any exception that may be assigned to the Throwable type. This includes the Error and Exception types.
A throw statement may throw any expression that may be assigned to the Throwable type.
The ActionEvent event is generated as the result of the clicking of a button.
The exception propagates up to the next higher level try-catch statement (if any) or results in the program's termination.
An uncaught exception results in the uncaughtException() method of the thread's ThreadGroup being invoked, which eventually results in the termination of the program in which it is thrown.
If a thread attempts to execute a synchronized method or synchronized statement and is unable to acquire an object's lock, it enters the waiting state until the lock becomes available.
The result is a String object.
When a task's interrupt() method is executed, the task enters the ready state. The next time the task enters the running state, an InterruptedException is thrown.
All AWT event listeners extend the java.util.EventListener interface.
An object must implement the Serializable or Externalizable interface before it can be written to a stream as an object.
After a thread is started, via its start() method or that of the Thread class, the JVM invokes the thread's run() method when the thread is initially executed.
A compilation unit is a Java source code file.
A Java package is a naming context for classes and interfaces. A package is used to create a separate name space for groups of classes and interfaces. Packages are also used to organize related classes and interfaces into a single API unit and to control accessibility to these classes and interfaces.
A layout manager is an object that is used to organize components in a container.
A native method is a method that is implemented in a language other than Java.
A task's priority is an integer value that identifies the relative order in which it should be executed with respect to other tasks. The scheduler attempts to schedule higher priority tasks before lower priority tasks.
A transient variable is a variable that may not be serialized.
A void return type indicates that a method does not return a value.
An abstract method is a method whose implementation is deferred to a subclass.
The Iterator interface is used to step through the elements of a Collection.
An object's lock is a mechanism that is used by multiple threads to obtain synchronized access to the object. A thread may execute a synchronized method of an object only after it has acquired the object's lock. All objects and classes have locks. A class's lock is acquired on the class's Class object.
There are two types of casting, casting between primitive numeric types and casting between object references. Casting between numeric types is used to convert larger values, such as double values, to smaller values, such as byte values. Casting between object references is used to refer to an object by a compatible class, interface, or array type reference.
Clipping is the process of confining paint operations to a limited area or shape.
Numeric promotion is the conversion of a smaller numeric type to a larger numeric type, so that integer and floating-point operations may take place. In numerical promotion, byte, char, and short values are converted to int values. The int values are also converted to long values, if necessary. The long and float values are converted to double values, as required.
With respect to multithreading, synchronization is the capability to control the access of multiple threads to shared resources. Without synchronization, it is possible for one thread to modify a shared object while another thread is in the process of using or updating that object's value. This often leads to significant errors.
It is referred to as the modulo or remainder operator. It returns the remainder of dividing the first operand by the second operand.
A program's main() method takes an argument of the String type.
If a checked exception may be thrown within the body of a method, the method must either catch the exception or declare it in its throws clause.
The Collections API is a set of classes and interfaces that support operations on collections of objects.
The Dictionary class provides the capability to store key-value pairs.
A Choice is displayed in a compact form that requires you to pull it down to see the list of available choices. Only one item may be selected from a Choice. A List may be displayed in such a way that several List items are visible. A List supports the selection of one or more List items.
A field variable is a variable that is declared as a member of a class. A local variable is a variable that is declared local to a method.
The CheckboxMenuItem class extends the MenuItem class to support a menu item that may be checked or unchecked.
A public class may be accessed outside of its package. A non-public class may not be accessed outside of its package.
A Scrollbar is a Component, but not a Container. A ScrollPane is a Container. A ScrollPane handles its own events and performs its own scrolling.
A non-static inner class may have object instances that are associated with instances of the class's outer class. A static inner class does not have any object instances.
The Frame class extends Window to define a main application window that can have a menu bar.
Under preemptive scheduling, the highest priority task executes until it enters the waiting or dead states or a higher priority task comes into existence. Under time slicing, a task executes for a predefined slice of time and then reenters the pool of ready tasks. The scheduler then determines which task should execute next, based on priority and other factors.
The >> operator carries the sign bit when shifting right. The >>> zero-fills bits that have been shifted out.
If an expression involving the Boolean & operator is evaluated, both operands are evaluated. Then the & operator is applied to the operand. When an expression involving the && operator is evaluated, the first operand is evaluated. If the first operand returns a value of true then the second operand is evaluated. The && operator is then applied to the first and second operands. If the first operand evaluates to false, the evaluation of the second operand is skipped.
The File class encapsulates the files and directories of the local file system. The RandomAccessFile class provides the methods needed to directly access data contained in any part of a file.
The FontMetrics class is used to define implementation-specific properties, such as ascent and descent, of a Font object.
The JDK 1.02 event model uses an event inheritance or bubbling approach. In this model, components are required to handle their own events. If they do not handle a particular event, the event is inherited by (or bubbled up to) the component's container. The container then either handles the event or it is bubbled up to its container and so on, until the highest-level container has been tried. In the event-delegation model, specific objects are designated as event handlers for GUI components. These objects implement event-listener interfaces. The event-delegation model is more efficient than the event-inheritance model because it eliminates the processing required to support the bubbling of unhandled events.
The prefix form performs the increment operation and returns the value of the increment operation. The postfix form returns the current value all of the expression and then performs the increment operation on that value.
The Reader/Writer class hierarchy is character-oriented, and the InputStream/OutputStream class hierarchy is byte-oriented.
String objects are constants. StringBuffer objects are not constants.
When a task invokes its yield() method, it returns to the ready state. When a task invokes its sleep() method, it returns to the waiting state.
The GregorianCalendar class provides support for traditional Western calendars.
The java.util.EventObject class is the highest-level class in the event-delegation class hierarchy.
The List interface provides support for ordered collections of objects.
The Map interface replaces the JDK 1.1 Dictionary class and is used associate keys with values.
The preferred size of a component is the minimum component size that will allow the component to display normally.
A statement block is used to organize a sequence of statements as a single statement group.
The purpose of finalization is to give an unreachable object the opportunity to perform any cleanup processing before the object is garbage collected.
The enableEvents() method is used to enable an event for a particular object. Normally, an event is enabled when a listener is added to an object for a particular event. The enableEvents() method is used by objects that handle events by overriding their event-dispatch methods.
The File class is used to create objects that provide access to the files and directories of a local file system.
The finally clause is used to provide the capability to execute code no matter whether or not an exception is thrown or caught.
The purpose of the Runtime class is to provide access to the Java runtime system.
The purpose of the System class is to provide access to system resources.
The wait(), notify(), and notifyAll() methods are used to provide an efficient way for threads to wait for a shared resource. When a thread executes an object's wait() method, it enters the waiting state. It only enters the ready state after another thread invokes the object's notify() or notifyAll() methods..
A method's throws clause must declare any checked exceptions that are not caught within the body of the method.
An event-listener interface defines the methods that must be implemented by an event handler for a particular kind of event. An event adapter provides a default implementation of an event-listener interface.
When a window is repainted by the AWT painting thread, it sets the clipping regions to the area of the window that requires repainting.
A Canvas object provides access to a Graphics object via its paint() method.
The ResourceBundle class is used to store locale-specific resources that can be loaded by a program to tailor the program's appearance to the particular locale in which it is being run.
A program's main() method has a void return type.
The Set interface provides methods for accessing the elements of a finite mathematical set. Sets do not allow duplicate elements.
The SimpleTimeZone class provides support for a Gregorian calendar.
The Vector class provides the capability to implement a growable array of objects
If you are running Java on English Windows platforms, it is probably Cp1252. If you are running Java on English Solaris platforms, it is most likely 8859_1.
The start() method of the Thread class is invoked to cause an object to begin executing as a separate thread.
The setLayout() method is used to specify a container's layout.
All tasks must implement the run() method, whether they are a subclass of Thread or implement the Runnable interface.
getLabel() and setLabel().
A top-level class may be public, abstract, or final.
A (non-local) inner class may be declared as public, protected, private, static, final, or abstract.
An interface may be declared as public or abstract.
It must provide all of the methods in the interface and identify the interface in its implements clause.
Two methods may not have the same name and argument list but different return types.
Overridden methods must have the same name, argument list, and return type. The overriding method may not limit the access of the method it overrides. The overriding method may not throw any exceptions that may not be thrown by the overridden method.
A package statement must appear as the first line in a source code file (excluding blank lines and comments).
During compilation, the values of each case of a switch statement must evaluate to a value that can be promoted to an int value.
When a thread terminates its processing, it enters the dead state.
An executing thread is in the running state.
The read() method returns -1 when it has reached the end of a file.
The readLine() method returns null when it has reached the end of a file.
The stop(), suspend() and resume() methods have been deprecated in JDK 1.2.
A thread enters the waiting state when it blocks on I/O.
A thread is in the ready state after it has been created and started.
An object reference be cast to an interface reference when the object implements the referenced interface.
The compiler supplies a default constructor for a class if no other constructors are provided.
An object is subject to garbage collection when it becomes unreachable to the program in which it is used.
The finally clause of the try-catch-finally statement is always executed unless the thread of execution terminates or an exception occurs within the execution of the finally clause.
Integer / and % can result in the throwing of an ArithmeticException.
The digits 0 through 9 may not be used as the first character of an identifier but they may be used after the first character of an identifier.
The Object class is extended by all other classes.
The Class class is used to obtain information about an object's design.
validate() method is used to cause a container to be laid out and redisplayed.
The Window, Frame and Dialog classes use a border layout as their default layout.
The Panel and Applet classes use the FlowLayout as their default layout.
The = operator is right associative.
The EventObject class and the EventListener interface support event processing.
The abs() method is used to calculate absolute values.
setBounds() method is used to set the position and size of a component.
The non-Unicode letter characters $ and _ may appear as the first character of an identifier
The java.lang package is always imported by default.
So they can be invoked as if they are a mathematical code library.
Threads block on I/O (that is enters the waiting state) so that other threads may execute while the I/O Operation is performed.