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Published bySimon Alexander Modified over 9 years ago
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Using the Java programming language compiler
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Review of relevant material from previous lectures From previous lectures: A computer can only execute machine instruction codes (binary numbers) Writing algorithms in machine instruction codes is extremely tedious
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Review of relevant material from previous lectures (cont.) People have invented a number of English-like languages that is highly suitable for writing algorithms People have also written computer applications that translate algorithm written in a programming language into machine instructions These languages are called (high level) programming languages These applications are called compilers
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How to write an algorithm that a computer can execute The hard way: You will hate your professor if he/she make you do this.... (and yet, the pioneers in Computer Science had done this... we must be grateful to them) Write the algorithm (yourself) in machine instruction (binary numbers)
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How to write an algorithm that a computer can execute (cont.) The easy way: 1.Write the algorithm (yourself) in a programming language (using an editor like gedit) 2.Translate the program using a compiler into machine instructions (The translated program is stored in a computer file) 3.Let the computer execute the translated program in machine instructions (This translated program is an computer application because it can be run by a computer)
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How to write an algorithm that a computer can execute (cont.) Pictorially: (An application is a file that contains machine instructions (which can be executed by a computer))
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Using the Java compiler The name of the Java compiler (application) is: javac
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Using the Java compiler (cont.) A Java program (= a computer algorithm written in the Java programming language) is first written and stored in a file The name of the file must end with the characters: The ending of a filename is called the file extension and it is commonly used to identify the kind of file..java
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Using the Java compiler (cont.) The following command will translate a Java program into machine code: The Java compiler javac will store the translated machine codes into a file name ProgramFileName.class UNIX prompt>> javac ProgramFileName.java
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Using the Java compiler (cont.) Example:
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Using the Java compiler (cont.) Example Program: (Demo above example) –The Hello.java Prog file: http://mathcs.emory.edu/~cheung/Courses/170/Syllabus/02/Progs/ Hello.java What to do: Right click of the link and save in some scratch directory Change current directory to that scratch directory Compile Hello.java with javac Hello.java
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The Java machine language The translated machine code produced by the Java compiler javac is called: Java bytecode
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The Java machine language Java bytecodes are executed by a Java machine --- a computer that executes machine instructions in Java bytecodes However, no such Java machine has ever been built In other words: There does not exist a physical computer (machine) that can execute Java byte codes
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The Java virtual machine Emulators: Emulators are also known as virtual machines (Because they do the same thing as a real machine, but is not a physical machine) Emulators are (special) computer programs that emulate the exact behavior of a machine or entity
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The Java virtual machine (cont.) Java virtual machine: (A Java virtual machine is an emulator) A Java virtual machine is a computer program (application) than can execute an algorithm written in Java bytecode
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The Java virtual machine (cont.) The name of this computer application is: java
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Executing the translated Java program with a Java virtual machine Suppose the program containing the Java bytecode is called: This program can be executed by the Java virtual machine java by executing the following command: ProgramFileName.clas s java ProgramFileName
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Executing the translated Java program with a Java virtual machine (cont.) Note: You must omit the extension.class The Java virtual machine java will append the extension.class to its argument
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Executing the translated Java program with a Java virtual machine (cont.) Example:
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Executing the translated Java program with a Java virtual machine (cont.) Example Program: (Demo above code) –Hello.java Prog file: http://mathcs.emory.edu/~cheung/Courses/170/Syllabus/02/Progs/ Hello.java What to do: Right click on the link ans save in some scratch directory Change current directory to that scratch directory Compile Hello.java with: &nsbp; javac Hello.java Then execute the Java bytecode Hello.class with: java Hello
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