Understanding the 'finally' block

Question

I've written seven test cases for understanding the behavior of the finally block. What is the logic behind how finally works?

package core;

public class Test {
    public static void main(String[] args) {
        new Test().testFinally();
    }

    public void testFinally() {
        System.out.println("One = " + tryOne());
        System.out.println("Two = " + tryTwo());
        System.out.println("Three = " + tryThree());
        System.out.println("Four = " + tryFour());
        System.out.println("Five = " + tryFive());
        System.out.println("Six = " + trySix());
        System.out.println("Seven = " + trySeven());
    }

    protected StringBuilder tryOne() {
        StringBuilder builder = new StringBuilder();
        try {
            builder.append("Cool");
            return builder.append("Return");
        }
        finally {
            builder = null;
        }
    }

    protected String tryTwo() {
        String builder = "Cool";
        try {
            return builder += "Return";
        }
        finally {
            builder = null;
        }
    }

    protected int tryThree() {
        int builder = 99;
        try {
            return builder += 1;
        }
        finally {
            builder = 0;
        }
    }

    protected StringBuilder tryFour() {
        StringBuilder builder = new StringBuilder();
        try {
            builder.append("Cool");
            return builder.append("Return");
        }
        finally {
            builder.append("+1");
        }
    }

    protected int tryFive() {
        int count = 0;
        try {
            count = 99;
        }
        finally {
            count++;
        }
        return count;
    }

    protected int trySix() {
        int count = 0;
        try {
            count = 99;
        }
        finally {
            count = 1;
        }
        return count;
    }

    protected int trySeven() {
        int count = 0;
        try {
            count = 99;
            return count;
        }
        finally {
            count++;
        }
    }
}

Why builder = null is not working?

Why does builder.append("+1") work whereas count++( in trySeven()) does not work?

Answer 1

StringBuilder cannot be null it expects a string value.

Null arguments are generally bad when working with strings. count++ isn't declared??? builder.append("") you are appending a string - good. count=count++;