reference: 'Java Statements', 'Just Java', van der Linden, 'Core Java', Hoorstman & Cornell

Statements express what a program does. Statements are typically grouped inside blocks,
constructors or methods. Most texts will try to organize the presentation of statements in
one way or another. Van der Linden's choice of categories is good, so we will follow suite
and present each statement type by whether they are organizing, expression, selection or
iteration statements.

Organizing Statements

1) The Block Statement is a pair of curly braces {   } containing zero or more local
    variables and statements.Wherever a single statement can be put, a block can be put.

Example 1  {
                // zero or more variables
                       // zero or more assignments, increments, method calls, new instances etc.
                 }

2) The Empty Statement is simply a semicolon by itself.

    ;

    It does nothing by itself which is sometimes what you want.

Example 2     boolean Rain = true;
                   if (Rain)
                     ;                   // if rain do nothing
                   else
                   go_swim( );    // assume this method is defined somewhere

Expression Statements

When an expression ends with a semi-colon, it is considered to be a statement.

Examples       JButton jb = new JButton("New button");     //  instance creation
                        jb.setLabel("Older Button");                     //  method call
                        ++ j ;                                                       //  pre increment
                        a = z;                                                       //  assignment
 
 

More on Expressions  An unreferenced, expression statement result is discarded. Recall an expression evaluates to a result, either a variable, value or a void. In the case that an expression is not assigned to a reference, the result is discarded    Example        new TextArea ("not referenced");             //  the resultant pointer is discarded                           panel.add (new TextArea ("not referenced") );   //  example again in a context

Selection Statements       // also referred to as conditional statements.
 

if  ( boolean expression )Statement  opt. [ else Statement ]

Example     boolean shootsLeft = true;
                     if  (shootsLeft)
                          make_Left_Wing("player's name");       // assume this method is callable
                        else
                         make_Right_Wing("player's name");

  //  to execute multiple  statements after an  if  block, enclose the statements in curly braces, { }

switch ( expression ) Statement // where expression is, or resolves to, a byte, char, short or int

Example   // notice the case statements end with a colon
               int i;
               for (i = 4;  i > 0; i--) {

                      switch ( i ){
                        case 4:
                         System.out.println("Ready");
                         break;
                         case 3:
                         System.out.println("On your marks");
                         break;
                         case 2:
                         System.out.println("Get set");
                         break;
                         case 1:
                         System.out.println("Go");
                         break;
                        default:
                         System.out.println("Restart");
                         }
                 }

If you leave break out, execution falls through to the next case. Note also, the default
statement is optional and can be placed anywhere in the switch construct.Where there is
no default and no case matches, nothing is printed out.
 

More on the switch The switch fallthrough feature is error-prone. Van der Linden also observes it is rarely used  feature.He did an interesting survey where he viewed 320 switches in the java source code,  observing less than 1% used the fallthrough feature. The implication is the behaviour should  have been left out of the construct and added optionally rather than the other way around.   Imitation of switch behaviour using if statements  class tif{  public static void main(String[]args){ int x=(int)(Math.random( )*3)+1;    if(x==1)    to("One");    if(x==2)    to("Two");    if(x==3)    to("Three");    } static void to(String s){   System.out.println(s);   } }

Iteration Statements

for  ( initialization   test condition   increment )

The for loop is sometimes called a determinate loop. Declarations can happen
inside or outside the for loop

Example        int i;
                   for ( i = 0; i< 99; i++)

       or          for (int i = 0; i< 99; i++)

Loops can contain compound initialization and increments

Example    for (int i = 0, j = 0 ; i < 100; i++ , j +=2 )

An infinite for loop  is created by leaving out the expressions of the for loop,
leaving two empty statements.

Example           for ( ; ; )
 
 

More on 'for'   class forT{      public static void main(String[] args){      // Good      int j=9;      System.out.println("\n First for loop \n");      for(int x=0; x<4;x++,j++){         System.out.println( x + "  " + j);         }       // Also OK     int k=0;      System.out.println("\n Second for loop \n");      for(int x=0, k=4; x<5;x++,k++){         System.out.println(x*2 + "  " + k*2);         }       // NOT good!        // You can't mix variable declarations inside expressions       /*      int q;      for(q=0, int w=4; q<10;q++,w++){         System.out.println(q + "  " + w);         }      */       }       }  // Summary  // There are only the three, semicolon-seperated regions   // in the for loop which internally can be compounded by   // comma seperation. You can't mix variable declarations // inside expressions.

while ( boolean expression ) Statement

The while and do...while statement are sometimes called indeterminate loops.While
the boolean expression is true the statement is executed. The loop iterates 0 or more
times. If the expression is false control passes to the first line of code past the statement.
If on first evaluation, the expression resolves to false the statement is never executed.

do  Statement  while  ( boolean expression )

The statement is executed at least once and then the expression is evaluated,
continuing while the boolean expression remains true.

continue  opt. label

continue moves the flow of control to the next iteration of a loop. It is only used in
loops.If used within nested loops, label can be placed to indicate which loop's next
iteration is executed.

break  opt. label

break is more 'extreme' then continue. It causes control to pass right out (to the end)
of the loop it is contained in. If used with a label, the break is to the end of the block
the label is attached to.

     Output

1  2  3  4  1  2  3  4  6  7  0 0   0 0   1 0  2 0 .

throw  -raises an exception and belongs in the discussion of Exceptions.
goto     -is reserved but not in use