/**
* Copyright (C) 2024 by Martin Robillard.
* See https://codesample.info/about.html
*/
essentials;
/**
* How the simplest possible Java program actually works.
*/
public
{
public static void (String[] args)
{
System.out.println();
}
}The "Hello, World" program has a famed history going back to the 1970s.
The "Hello, World" program has a famed history going back to the 1970s.
Any Java source code must be placed in a class, no matter what it does. The only exceptions are package declarations and import statements.
Any Java source code must be placed in a class, no matter what it does. The only exceptions are package declarations and import statements.
System.out
is a static field. It contains a value of type
PrintStream
that represents the standard output normally visible on a terminal console. Calling println
on this object thus "prints" the argument to the standard system console.
Printing to the console is just a special case of printing to a PrintStream. It is also possible to print to other
print streams, such as to files.
System.out
is a static field. It contains a value of type
PrintStream
that represents the standard output normally visible on a terminal console. Calling println
on this object thus "prints" the argument to the standard system console.
Printing to the console is just a special case of printing to a PrintStream. It is also possible to print to other
print streams, such as to files.
Although Java does not have an explicit mechanism to define global variables,
fields that are declared both and serve this purpose because they can be accessed from anywhere in the code.
Although Java does not have an explicit mechanism to define global variables,
fields that are declared both and serve this purpose because they can be accessed from anywhere in the code.
An element preceded with the keyword public can be accessed by any other code.
An element preceded with the keyword public can be accessed by any other code.
A field preceded with the keyword static is not associated with any particular object. Instead, it is a variable placed in the scope of the entire running application.
A field preceded with the keyword static is not associated with any particular object. Instead, it is a variable placed in the scope of the entire running application.
"Hello, World!" is a string literal value.
"Hello, World!" is a string literal value.
"A package a grouping of related types providing access protection and name space management." Source code files in a package must be placed in a directory with the same name as the package, and a package declaration must be placed at the top of the file.
"A package a grouping of related types providing access protection and name space management." Source code files in a package must be placed in a directory with the same name as the package, and a package declaration must be placed at the top of the file.
void is a keyword used in place of a return type to indicate that a method does not return a value.
void is a keyword used in place of a return type to indicate that a method does not return a value.
This is the only element that can change from the header declaration of a main method: the name of the parameter can be any valid Java identifier.
This is the only element that can change from the header declaration of a main method: the name of the parameter can be any valid Java identifier.
The main method must have a single parameter, which must be an array of String. The values of this array are supplied when starting the program, typically through the command line. This type can also be expressed as a vararg (variable arguments), written as String....
The main method must have a single parameter, which must be an array of String. The values of this array are supplied when starting the program, typically through the command line. This type can also be expressed as a vararg (variable arguments), written as String....
System class contains several useful class fields and methods. It cannot be instantiated. Among the facilities provided by the System class are standard input, standard output, and error output streams; access to externally defined properties and environment variables; a means of loading files and libraries; and a utility method for quickly copying a portion of an array.
System class contains several useful class fields and methods. It cannot be instantiated. Among the facilities provided by the System class are standard input, standard output, and error output streams; access to externally defined properties and environment variables; a means of loading files and libraries; and a utility method for quickly copying a portion of an array.
Console.charset() if the Console exists, stdout.encoding otherwise.
Console.charset() if the Console exists, stdout.encoding otherwise.
For simple stand-alone Java applications, a typical way to write a line of output data is:
System.out.println(data)
See the println methods in class PrintStream.
print(String) and then println().
print(String) and then println().
x - The String to be printed.
String class represents character strings. All string literals in Java programs, such as "abc", are implemented as instances of this class.
String class represents character strings. All string literals in Java programs, such as "abc", are implemented as instances of this class.
Strings are constant; their values cannot be changed after they are created. String buffers support mutable strings. Because String objects are immutable they can be shared. For example:
String str = "abc";
is equivalent to:
char data[] = {'a', 'b', 'c'};
String str = new String(data);
Here are some more examples of how strings can be used:
System.out.println("abc");
String cde = "cde";
System.out.println("abc" + cde);
String c = "abc".substring(2, 3);
String d = cde.substring(1, 2);
The class String includes methods for examining individual characters of the sequence, for comparing strings, for searching strings, for extracting substrings, and for creating a copy of a string with all characters translated to uppercase or to lowercase. Case mapping is based on the Unicode Standard version specified by the Character class.
The Java language provides special support for the string concatenation operator ( + ), and for conversion of other objects to strings. For additional information on string concatenation and conversion, see The Java Language Specification.
Unless otherwise noted, passing a null argument to a constructor or method in this class will cause a NullPointerException to be thrown.
A String represents a string in the UTF-16 format in which supplementary characters are represented by surrogate pairs (see the section Unicode Character Representations in the Character class for more information). Index values refer to char code units, so a supplementary character uses two positions in a String.
The String class provides methods for dealing with Unicode code points (i.e., characters), in addition to those for dealing with Unicode code units (i.e., char values).
Unless otherwise noted, methods for comparing Strings do not take locale into account. The Collator class provides methods for finer-grain, locale-sensitive String comparison.
javac compiler may implement the operator with StringBuffer, StringBuilder, or java.lang.invoke.StringConcatFactory depending on the JDK version. The implementation of string conversion is typically through the method toString, defined by Object and inherited by all classes in Java.