Which of the following is a valid way to declare a variable in Java?

In Java, declaring a variable requires specifying its type followed by its name, and optionally assigning a value. The correct answer demonstrates the proper syntax for variable declaration and initialization.

In this case, using "int x = 10;" is valid because it starts with the type "int," which indicates that the variable x will store an integer value. The assignment operator "=" is used to assign the value 10 to the variable x at the moment of declaration. This approach initializes the variable while also defining its data type, which is necessary for Java's statically typed nature.

Declaring a variable properly is crucial because it ensures that the program knows what kind of data the variable will hold, thus helping to prevent errors during runtime. This validity is a fundamental aspect of strong typed languages like Java, where each variable must have a clearly defined type.

The other options do not follow the correct syntax. For example, using "int x" without assigning a value means the variable x is declared but not initialized, which is technically valid but not complete. The choice of "var x = 10;" would be valid in some Java environments where type inference is allowed, but traditional Java prefers explicit type declarations with "int" or other types. Lastly, "x