Java Statements

Java statements is the most fundamental topic to master to be an effective Java programmer.
Four types of statements are:

Assignment Statement:
Assignment statements of all primitives will return their primitive values.
1. Value can be assigned as shown below
int a;
int b;
a = (b=true);


2. common type of assigning value is
int a = 9;

3. Remember that the only valid literal values for the boolean primitives are true and false. Below statements are invalid
boolean isValid = TRUE;

boolean isValid = 1;

Conditional Statement:
Valid scenarios
1. true  or false statements and the following type of assignment statement is correct inside a if statement.
boolean a = false;
if(a = true)
{}

2. Boolean wrapper class can be used as unboxing is the automatic production of its primitive value in cases where it is needed. So the following code is correct.
Boolean wrapperBoolean = new Boolean("true");
if(wrapperBoolean)
{}

3. Order does not matter in the switch cases. If a case is satisfied then default is ignored.
int a = 1;
switch(a)
{
  default:
     System.out.println("Default executed first");
  case 1:
     System.out.println("a executed first");
}
Output:  a executed first

4. String can be used in cases starting Java 7

String a = "hello";

switch(a)

{

    default:

        System.out.println("Default executed first");

        break;

    case "1":

        System.out.println("1 executed first");

        break;

    case "hello":

        System.out.println("hello executed first");

        break;

}

Output: hello executed first

5. Arithmetic operations are allowed in case as shown below
int a = 2;
switch(a)
{
    default:
        System.out.println("Default executed first");
        break;
    case 3-1:
        System.out.println("2 executed first");
        break;

}
Output: 2 executed first

6. Switch fall through can be taken advantage because all the cases following a success case without a break will get executed. Eg of fallthrough is shown below

public class SwitchDemoFallThrough {

    public static void main(String[] args) {
        java.util.ArrayList futureMonths =
            new java.util.ArrayList();

        int month = 8;

        switch (month) {
            case 1:  futureMonths.add("January");
            case 2:  futureMonths.add("February");
            case 3:  futureMonths.add("March");
            case 4:  futureMonths.add("April");
            case 5:  futureMonths.add("May");
            case 6:  futureMonths.add("June");
            case 7:  futureMonths.add("July");
            case 8:  futureMonths.add("August");
            case 9:  futureMonths.add("September");
            case 10: futureMonths.add("October");
            case 11: futureMonths.add("November");
            case 12: futureMonths.add("December");
                     break;
            default: break;
        }

        if (futureMonths.isEmpty()) {
            System.out.println("Invalid month number");
        } else {
            for (String monthName : futureMonths) {
               System.out.println(monthName);
            }
        }
    }
}

This is the output from the code:

August
September
October
November
December

7. Following statement compiles without any problem.
if (x == 0) ; else if (x == 1){} else {;}

8. Following statements compiles without any problem.
if (true) ;
if (true) {}
if (true) {;}
if (true) {;;}
if (true) ;{};

Invalid scenarios
1. Since assignment statements return their primitive values, following code will fail to compile
int a = 1;
if(a = 2)
{}

2. Ranges are not allowed in cases.

3.Following statement throws compilation error because no space between elseif
if (x == 0) {;} elseif (x == 1) {System.out.println("Valid Statement");}