Java Tutorials

Understanding the Structure of a Java Program

Understanding the Structure of a Java Program

The following are the main parts of a typical Java program:

  • Class Definition
  • Main Method
  • Statements and Expressions

Let us examine the structure of our sample program:

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }
}

Class Definition

A class named HelloWorld is defined by the public class HelloWorld. Each element of code must be contained within a class in Java. The keyword "public" is an access modifier that authorizes any other class to access the class.

Main Method

static, public void main(String[] args): This initiates the program's execution.

  • Public: This defines the method as accessible from outside the class.
  • static: In other words, the method is a member of the class, not an instance of the class. The class can be invoked without the need to create an object.
  • Void: The method is considered void if it does not return any value.
  • 'main' is the name of the procedure. This method is unique and functions as the application's entrance point.
  • string[]args: This is an array of strings that contains the command-line parameters that were provided to the program.

Statements and Expressions

`System.out.println("Hello, World!");`: This statement outputs text to the console.

  • System: A class that is predefined and grants access to the system.
  • in: an instance of PrintStream that is an intrinsic member of the System class.
  • println: A method of the PrintStream type. The specified string is printed to the console, with a newline character at the conclusion.

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Java

Beginner 5 Hours

Understanding the Structure of a Java Program

The following are the main parts of a typical Java program:

  • Class Definition
  • Main Method
  • Statements and Expressions

Let us examine the structure of our sample program:

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }
}

Class Definition

A class named HelloWorld is defined by the public class HelloWorld. Each element of code must be contained within a class in Java. The keyword "public" is an access modifier that authorizes any other class to access the class.

Main Method

static, public void main(String[] args): This initiates the program's execution.

  • Public: This defines the method as accessible from outside the class.
  • static: In other words, the method is a member of the class, not an instance of the class. The class can be invoked without the need to create an object.
  • Void: The method is considered void if it does not return any value.
  • 'main' is the name of the procedure. This method is unique and functions as the application's entrance point.
  • string[]args: This is an array of strings that contains the command-line parameters that were provided to the program.

Statements and Expressions

`System.out.println("Hello, World!");`: This statement outputs text to the console.

  • System: A class that is predefined and grants access to the system.
  • in: an instance of PrintStream that is an intrinsic member of the System class.
  • println: A method of the PrintStream type. The specified string is printed to the console, with a newline character at the conclusion.

Related Tutorials

Frequently Asked Questions for Java

Java is known for its key features such as object-oriented programming, platform independence, robust exception handling, multithreading capabilities, and automatic garbage collection.

The Java Development Kit (JDK) is a software development kit used to develop Java applications. The Java Runtime Environment (JRE) provides libraries and other resources to run Java applications, while the Java Virtual Machine (JVM) executes Java bytecode.

Java is a high-level, object-oriented programming language known for its platform independence. This means that Java programs can run on any device that has a Java Virtual Machine (JVM) installed, making it versatile across different operating systems.

Deadlock is a situation in multithreading where two or more threads are blocked forever, waiting for each other to release resources.

Functional programming in Java involves writing code using functions, immutability, and higher-order functions, often utilizing features introduced in Java 8.

A process is an independent program in execution, while a thread is a lightweight subprocess that shares resources with other threads within the same process.

The Comparable interface defines a natural ordering for objects, while the Comparator interface defines an external ordering.

The List interface allows duplicate elements and maintains the order of insertion, while the Set interface does not allow duplicates and does not guarantee any specific order.

String is immutable, meaning its value cannot be changed after creation. StringBuffer and StringBuilder are mutable, allowing modifications to their contents. The main difference between them is that StringBuffer is synchronized, making it thread-safe, while StringBuilder is not.

Checked exceptions are exceptions that must be either caught or declared in the method signature, while unchecked exceptions do not require explicit handling.

ArrayList is backed by a dynamic array, providing fast random access but slower insertions and deletions. LinkedList is backed by a doubly-linked list, offering faster insertions and deletions but slower random access.

Autoboxing is the automatic conversion between primitive types and their corresponding wrapper classes. For example, converting an int to Integer.

The 'synchronized' keyword in Java is used to control access to a method or block of code by multiple threads, ensuring that only one thread can execute it at a time.

Multithreading in Java allows concurrent execution of two or more threads, enabling efficient CPU utilization and improved application performance.

A HashMap is a collection class that implements the Map interface, storing key-value pairs. It allows null values and keys and provides constant-time performance for basic operations.

Java achieves platform independence by compiling source code into bytecode, which is executed by the JVM. This allows Java programs to run on any platform that has a compatible JVM.

The Serializable interface provides a default mechanism for serialization, while the Externalizable interface allows for custom serialization behavior.

The 'volatile' keyword in Java indicates that a variable's value will be modified by multiple threads, ensuring that the most up-to-date value is always visible.

Serialization is the process of converting an object into a byte stream, enabling it to be saved to a file or transmitted over a network.

The finalize() method is called by the garbage collector before an object is destroyed, allowing for cleanup operations.

The 'final' keyword in Java is used to define constants, prevent method overriding, and prevent inheritance of classes, ensuring that certain elements remain unchanged.

Garbage collection is the process by which the JVM automatically deletes objects that are no longer reachable, freeing up memory resources.

'throw' is used to explicitly throw an exception, while 'throws' is used in method declarations to specify that a method can throw one or more exceptions.

The 'super' keyword in Java refers to the immediate parent class and is used to access parent class methods, constructors, and variables.

The JVM is responsible for loading, verifying, and executing Java bytecode. It provides an abstraction between the compiled Java program and the underlying hardware, enabling platform independence.

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