Lecture 3: Scaffolding and Output

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Last Time• Acquiring &

creating language• Noam Chomsky• Catherine Snow

Lecture 3: Scaffolding and Output

Today

Compilation and Execution– What’s “javac” do? – What happens next?

Basics– Scaffolding - what every program

needs– Making the computer talk to you!

Lecture 3: Scaffolding and Output

Static Compilation & Execution

Easier case: The C programming language “static” ahead-of-time compilation model:

Tool: “cc” the C compilerYour file: Circle.c

“cc Circle.c” -> (Circle.a) -> a.outExecutable: a.out

“a.out”

Lecture 3: Scaffolding and Output

Dynamic Compilation & Execution

Java “dynamic” compilation model:2 Tools

“javac” the Java bytecode compiler“java” the Java virtual machine

Your file: Circle.javaWhat do you do in Bluej?“javac Circle.java” -> Circle.class

Executing Bytecode: low-level virtual machine form machine independent, portableWhat do you do in Bluej?“java Circle.class”

Lecture 3: Scaffolding and Output

Java Dynamic Compilation

Executing Bytecode: “java Circle.class” What happens?

Interpretation vs Dynamic Compilation

Lecture 3: Scaffolding and Output

Dynamic Compilation & Execution

Java “dynamic” compilation model:Executing Bytecode:

“java Circle.class” - What happens?Interpreting 1. map each bytecode to a machine code

sequence,2. for each bytecode, execute the sequenceTranslation to machine code1. map all the bytecodes to machine code (or a

higher level intermediate representation),2. massage them (e.g., get rid of redundancies

between instructions), 3. execute the machine code

Lecture 3: Scaffolding and Output

Dynamic Compilation & Execution

“Hotspot” compilation, a hybrid 1. Initially interpret2. Find the “hot” (frequently executed

code) methods, and translate only these hot methods to machine code

Lecture 3: Scaffolding and Output

Basics

What you write– Scaffolding - what every program needs– Making the computer talk to you!

Comments - tell the compiler to ignore text// the compiler ignores this text on the same line

/* For multi-line comments, you can use * this form and it will ignore all this text

* too until it sees */

Lecture 3: Scaffolding and Output

Scaffolding:Magic or Logical?

/* Kathryn S McKinley * January 10, 2005 * file: Song.java * My program does nothing right now! */public class Song{ // code can go here

public static void main (String [] args) { // code here too }}

Lecture 3: Scaffolding and Output

Printing

System.out.print(“I love CS305j.”);

System.out.println(“I love CS305j.”);

[More examples in Bluej…]

Lecture 3: Scaffolding and Output

Questions?