How to generate loops and conditionals using the codemodel library

Question

I've been trying to learn how to use Suns codemodel library and I'm absolutely stumped with generating for loops and if-else blocks. I'm struggling with how to generate the conditions for the if-else blocks and the for loops, but also on how to generate the body of these as well.

For example:

if (condition) { //How is this condition generated?
     //How is this body filled?
} else {

} 

For the loop:

for(condition) {  //How is this condition generated?
   //How is this body filled?
}

Answer 1

Im going to assume you already have a class and method defined.

To write a condition if/else statement you need to use the _if() and _else() methods on the JBody class. This adds the statement to the body of the method you have defined. from these methods you can reference and add to their bodies by calling the _then() method on the _if() or _else() returns the JBody directly. Here's an example:

JConditional condition = body._if(input.lt(JExpr.lit(42)));
condition._then().add(
    codeModel.ref(System.class).staticRef("out").invoke("println").arg(JExpr.lit("hello"))); 
condition._else().add(
    codeModel.ref(System.class).staticRef("out").invoke("println").arg(JExpr.lit("world")));

which outputs:

if (input< 42) {
    System.out.println("hello");
} else {
    System.out.println("world");
}

To write a for loop, there are a couple of options. The traditional for loop is written using the _for() method on the JBlock, which allows you to chain the init(), test() and update() methods corresponding to the various parts of the for loop declaration:

JForLoop forLoop = body._for();
JVar ivar = forLoop.init(codeModel.INT, "i", JExpr.lit(0));
forLoop.test(ivar.lt(JExpr.lit(42)));
forLoop.update(ivar.assignPlus(JExpr.lit(1)));

forLoop.body().add(
    codeModel.ref(System.class).staticRef("out").invoke("println").arg(ivar));

which outputs:

for (int i = 0; (i< 42); i += 1) {
    System.out.println(i);
}

For kicks, here's a working example: https://gist.github.com/johncarl81/7647146