Example shows the difference between ++d and d++ operators.

Test.java

package test;

public class Test {
	// Example showing the difference between pre-increment (++i) and post-increment (i++) operators.
	public static void main(String[] args) {
		int d = 0;
		// d++ is post-increment op
		int e = d++; // What is the value of d and e after this line executes? It is d == 1 and e == 0
		if (e == 0) {
			System.out.println("d++ will first return the current value of d (which is 0) and assign it to e, then it will increment d to 1.");
		}
		
		// reset
		d = 0;
		// ++d is pre-increment op
		int f = ++d; // What is the value of d and f after this line executes? It is d == 1 and f == 1
		if (f == 1) {
			System.out.println("++d will first increment d to 1 and then assign that value to variable f.");
		}
		
		// Conclusion: Best way to remember the difference between ++d and d++ is this:
		// 1. Ask yourself where is ++ in relation to d (BEFORE or AFTER).
		// 2. The answer to that fills in the blank to the following statement:
		//		"The incrementing happens ______ the surrounding expression evaluates.


		// Simulate the pre-increment and post-increment operators with Java functions and classes
		IntegerWrapper w1 = new IntegerWrapper(0);
		
		int a = postInc(w1); // read: w1++. after this line executes: a == 0 and w1 == 1
		System.out.println("a == "+a+" and w1 == "+w1.i);
		
		// reset
		w1.i = 0;
		int b = preInc(w1); // read: ++w1. after this line executes: b == 1 and w1 == 1
		System.out.println("b == "+b+" and w1 == "+w1.i);
	}
	
	// Java implementation of ++i
	private static int preInc(IntegerWrapper iw) {
		iw.i = iw.i + 1;
		return iw.i;
	}
	
	// Java implementation of i++
	private static int postInc(IntegerWrapper iw) {
		int temp = iw.i;
		iw.i = iw.i + 1;
		return temp;
	}	
}

class IntegerWrapper {
	public int i;
	
	public IntegerWrapper(int i) {
		this.i = i;
	}
}