For-loop type – can’t recognise it

It’s a basic for loop.

It is documented in the Java Language Specification, section 14.14.1. The basic for Statement:

BasicForStatement:
  for ( [ForInit] ; [Expression] ; [ForUpdate] ) Statement

ForInit:
  StatementExpressionList
  LocalVariableDeclaration

ForUpdate:
  StatementExpressionList

StatementExpressionList:
  StatementExpression {, StatementExpression} 

Normally, you’ll see it like this:

ForInit:      int i = 0   // LocalVariableDeclaration
Expression:   i < 10
ForUpdate:    i++         // StatementExpression

for ( int i = 0 ; i < 10 ; i++ ) {
    // code
}

// mostly the same as:
int i = 0;
while ( i < 10 ) {
    // code
    i++;
}

^{Mostly the same, since the scope of i is limited to the loop, and the continue statement will go to the i++ statement, not directly back to the loop.}

But as you can see, all 3 are optional, where ForInit can be a statement list instead of a variable declaration, and Expression defaults to true.

ForInit:      In.init()   // StatementExpression
Expression:   !In.empty()
ForUpdate:                // not present

for ( In.init() ; !In.empty() ;  ) {
    // code
}

// same as:
In.init();
while ( !In.empty() ) {
    // code
}

The Expression defaulting to true means that the following are the same. I personally prefer the first, since for (;;) almost reads like “forever”.

for (;;) { // loop forever
    // code
}

while (true) { // loop forever
    // code
}