// declare_vs_assign: David I. Schwartz 1/2000

public class declare_vs_assign {
    public static void main(String[] args) {

	// Declare a variable called s
	// Variable now has a memory location and type
	//    but not necessarily a value

	String s;

	// Try the following code:
	// System.out.println("Testing before assign: " + s);

	// What happens? Using a variable before assigning makes Java upset.
	// Java produces an error, like:
	// declare_vs_assign.java:11: Variable s may not have been initialized.
	//		System.out.println("Testing before assign: " + s);
	// 1 error

	// Currently, what does Java see as s? An empty location:
	// __s__
	// |   |  <== no value inside s location
	// |___|  <== Java expects a String to go there, though!

	// Now, assign the variable s
	// Store a value inside the variable by using assignment
	// Syntax: variable = value or expression
	//         the left hand side (LHS) is variable
	//         the right hand side (RHS) is a value or expression
	// Java treats the assignment as LHS <- RHS,
	//    where LHS stores the value of RHS.
	// Note that Java must evaluate RHS before assigning it to LHS.

	s = "Hello, world!";
	System.out.println("Testing1 after assign: " + s);

	// Currently, what does Java see as s? An filled location:
	// ______s_____
	// | "Hello,  |  <== no value inside s location
	// |  World!" |  <== Java expects a String to go there, though!
	// |__________|

	
	// Demonstrate version with an expression in the RHS:
	s = "Hello," + " world!";
	System.out.println("Testing2 after assign: " + s);
	
    }

}

/* Output:

Testing1 after assign: Hello, world!
Testing2 after assign: Hello, world!

*/