Top 50 Java Developer Interview Questions You Must Prepare 03.Feb.2023

The Collections API is a set of classes and interfaces that support operations on collections of objects.

The wait(),notify(), and notifyAll() methods are used to provide an efficient way for threads to communicate each other in Java Programming.

It must provide all of the methods in the interface and identify the interface in its implements clause.

The FontMetrics class is used to define implementation-specific properties, such as ascent and descent, of a Font object.

No, it doesn't. 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 Iterator interface is used to step through the elements of a Collection.

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.

Operator & has no chance to skip both sides evaluation and && operator does. 

The GregorianCalendar provides support for traditional Western calendars in Java Programming.

The primitive types are byte, char, short, int, long, float, double, and boolean.

When a thread terminates its processing, it enters the dead state.

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 SimpleTimeZone class provides support for a Gregorian calendar in Java Programming.

A (non-local) inner class may be declared as public, protected, private, static, final, or abstract.

A trient variable is a variable that may not be serialized.

The sizeof operator is not a keyword in Java Programming.

The Map interface replaces the JDK 1.1 Dictionary class and is used associate keys with values.

It uses those low order bytes of the result that can fit into the size of the type allowed by the operation.

Unicode requires 16 bits and ASCII require 7 bits. Although the ASCII character set uses only 7 bits, it is usually represented as 8 bits. UTF-8 represents characters using 8, 16, and 18 bit patterns. UTF-16 uses 16-bit and larger bit patterns.

The purpose of the System class is to provide access to system resources in Java Programming.

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.

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 window, Frame and Dialog classes use a border layout as their default layout in Java Programming.

The Vector class in Java Programming provides the capability to implement a growable array of objects.

A catch clause can catch any exception that may be assigned to the Throwable type. This includes the Error and Exception types.

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.

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.

The List interface provides support for ordered collections of objects.

An anonymous class may implement an interface or extend a superclass, but may not be declared to do both.

The preferred size of a component is the minimum component size that will allow the component to display normally.

The finally clause is used to provide the capability to execute code no matter whether or not an exception is thrown or caught.

Wrapped classes are classes that allow primitive types to be accessed as objects.

The Canvas, Frame, Panel, and Applet classes support painting.

The properties class is a subclass of Hashtable that can be read from or written to a stream. It also provides the capability to specify a set of default values to be used.

Heavy weight components like Abstract Window Toolkit (AWT), depend on the local windowing toolkit. For example, java.awt.Button is a heavy weight component, when it is running on the Java platform for Unix platform, it maps to a real Motif button. In this relationship, the Motif button is called the peer to the java.awt.Button. If you create two Buttons, two peers and hence two Motif Buttons are also created. The Java platform communicates with the Motif Buttons using the Java Native Interface.

For each and every component added to the application, there is an additional overhead tied to the local windowing system, which is why these components are called heavyweight.

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 Panel and Applet classes use the FlowLayout as their default layout.

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.

A class that is declared without any access modifiers is said to have package or friendly access. This me that the class can only be accessed by other classes and interfaces that are defined within the same package.

Object class is the superclass for every class in Java Programming.

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.

An object reference be cast to an interface reference when the object implements the referenced interface.

for(;;)-for loop; while(true)-always true, etc.

Yes, a lock can be acquired on a class. This lock is acquired on the class's Class object.

The purpose of the Runtime class is to provide access to the Java runtime system in Java Programming.

validate();  : Container method is used to cause a container to be laid out and redisplayed in Java Programming.

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.

Java uses layout managers to lay out components in a consistent manner across all windowing platforms. Since Java's layout managers aren't tied to absolute sizing and positioning, they are able to accommodate platform-specific differences among windowing systems.

The Frame class extends Window to define a main application window that can have a menu bar.

The purpose of finalization is to give an unreachable object the opportunity to perform any cleanup processing before the object is garbage collected.

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.