23/02/15. Compile, execute, debug. Advanced Programming THE JAVA PLATFORM

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1 Advanced Programming THE JAVA PLATFORM What do you need to run your java application? G: STARTING A JAVA APPLICATION Compile, execute, debug Safari book collection at UNIBZ: Schildt, H. Java the complete reference, 9 th edition (2104) proquest.safaribooksonline.com/book/programming/java/

2 Machine code Machine code Machine code: set of instructions executed directly CPU Every processor or processor family has its own machine code instruction set Machine code Instructions are patterns of bits that by physical design correspond to different commands to the machine Example of machine instruction (R-type operation) Adding register 1 and 2 and placing to register 6; funct describes the operation [ op rs rt rd shamt funct] decimal binary 2

3 Running on different machines Systems may also differ in other details, such as memory arrangement, operating systems, or peripheral devices. Because a program normally relies on such factors, different systems will typically not run the same machine code, even when the same type of processor is used Compilation and execution Compiler: faster Directly to machine code good compilers can perform optimisations Interpreter: portable They are independent from the CPU Example Interpretation Example: how can the following statement be executed? A[i][j] = 1; Create a software environment that understands 2-dimensional array (and the language) To execute the statement, just put 1 in the array entry A[i][j]; 23/02/15 COP4020 Spring

4 Interpretation This is interpretation since the software environment understands the language and performs the operations specified by interpreting the statements. Example Compilation Example: how can the following statement be executed? A[i][j] = 1; Translate the statements into native machine (or assembly language) and then run the program. COP4020 Spring /02/15 Compilation and interpretation In general, which approach is more efficient? A[i][j] = 1; Compilation: salq $2, %rax addq %rcx, %rax leaq 0(,%rax,4), %rdx addq %rdx, %rax salq $2, %rax addq %rsi, %rax movl $1, A(,%rax,4) Interpretation: create a software environment that understand the language put 1 in the array entry A[i][j]; COP4020 Spring /02/15 4

5 Java Standard Edition Platform- JSE Specifications Development Tools to compile, run, monitor, debug, and document an application Application Programming Interface - API Deployments tools User Interface Toolkits Integration Libraries The Java Platform SoftwareDevelopmentKit(SDK) JavaRunTimeEnvironment(JRE) Source Byte Code JavaCompiler Code ClassLoader (.java) (javac) (.class) ByteCode Verifier JavaVirtual MachinewithJIT Compiler HotSpot OperatingSystem Machine Code Oracle implementation of JSE 5

6 Java commands javac java jdb JVM Load, Link, Resolve, and Source Code JavaCompiler (.java) (javac) Initialise classes and interface SoftwareDevelopmentKit(SDK) JavaRunTimeEnvironment(JRE) Byte Code ClassLoader (.class) ByteCode Verifier JavaVirtual MachinewithJIT Compiler HotSpot OperatingSystem Machine Code Solution Loading is the process of finding the binary representation of a class or interface type with a particular name and creating a class or interface file from that binary representation. If such class file is not found the the loading throws the exception: ClassNotFoundException Linking verifies and prepares the correctness of a type so that it can be executed. Preparing allocates memory for the static field of classes and interfaces and initialise them to their default values. Verification ensures that the binary representation of a class is structurally correct. Resolve. Resolution associate references to run-time values. Initialise classes and interfaces. Initialisation defines the values of class or interface variables. 6

7 Just in time compilation Programs spend almost all of their time executing a relatively small part of the code again and again. The chunk of code that is executed repeatedly may only be a small percent of the total program, but its behaviour determines the program's overall performance. Adaptive compilation The adaptive compilation first profiles the code while it is executing, to see what parts are being executed repeatedly. Adaptive compilation Once it knows it, it translates only these sections into machine code. Since it only compiles a small portion of the bytecode, it can afford to take the time necessary to optimise those portions. The rest of the program may not need to be compiled at all - just interpreted - saving memory and time. 7

8 Debugging The process to find and fix errors There can be compile time and run-time errors Than there are failures Command line examples Java SE 8 Includes for instance Lambda Expressions tutorial/java/javaoo/lambdaexpressions.html The javadoc tool supports the new DocTree API that enables you to traverse Javadoc comments as abstract syntax trees. 8