What is byte code in java

What is the use of Byte code in java

In a sense, the JVM is an interpreter, so Java bytecode in interpreted, while Java code code is compiled. JVM compiles complete byte code to machine code.

Why the Java language need bytecode? Why java design in this way?

As I know a java developer, need to let their . java file to become .class, and the .class requires the JVM to convert to native code to execute. Why the Java design in this way? Why don’t just as a scripting language , using a interpreter, to interpreter .java file? or why don’t just convert it to executable like C? Why need to convert to bytecode? What is the design philosophy behind the java language?

It is for sake of speed and portability at the same time.

All of what I am going to say is to be adapted and moderated depending on the case, but roughly:

• If you merely interpret the java file with an interpreter you would have portability but not speed .
• If you have to compile the code for a given processor architecture you would have speed but not portability .
• With the bytecode, you compile the code (into bytecode) for a common machine that will execute it (the JVM) it is a compromise between speed and portability .

Why the Java design in this way?

Write once, run everywhere — portability.

Why don’t just as a scripting language, using a interpreter, to interpreter .java file?

Performance. Bytecode can be compiled to native code with some aggressive optimizations, not available for normal compilers.

or why don’t just convert it to executable like C?

Because different platforms require different executable binaries. Java bytecode is (again) portable.

Why don’t just as a scripting language, using a interpreter, to interpreter .java file? or why don’t just convert it to executable like C? Why need to convert to bytecode?

I think the intention was to have

1) Compile time safety
2) Write once, run anywhere.

If you converted to an executable like C, you would lose #2. In a sense, the JVM is an interpreter, so Java bytecode in interpreted, while Java code code is compiled.

Why don’t just as a scripting language, using a interpreter, to interpreter .java file?

or why don’t just convert it to executable like C?

Because that won’t work cross-platform. A Portable Executable (used on Windows) won’t run on, say, Linux or iOS, at least not without tricks.

A simple comparison can be made by thinking of sockets and file access. How would you do that on different platforms, with one executable, without the JVM?

Just In Time Compiler, The Just-In-Time (JIT) compiler is an essential part of the JRE i.e. Java Runtime Environment, that is responsible for performance

What is Java Bytecode ?

bytecode #javabytecode #javaprogramming #machinecode #javacompiler #jvmThis video
Duration: 6:11

What is Bytecode in Java ?

What is Byte Code ? Why Java’s intermediary Code is called Byte Code ?Check my free mini Duration: 4:49

What is Bytecode? Explain Bytecode, Define Bytecode, Meaning of

Unlike human-readable source code, bytecodes are compact numeric codes, constants, and Duration: 1:33

Import statement byte code significance

Lets say , there are some import statements in a class. When the byte code is generated for that class, what happens to these import statements.

If the import statements are ignored during runtime, how are the dependencies on that classes methods resolved during runtime.

The purpose of import statements is just to make life easier for the human readers (and authors) of the code. Thus they are replaced by references to the fully qualified class/method names in the bytecode. And unused import statement s are ignored.

import in Java is just a shorthand

so that if you import java.util.* you don’t have to write java.util.ArrayList in your code but can write ArrayList

import statements are only there for the compiler so it knows what class names (or static method names) you can access unqualified in your code (i.e. MyClass instead of ****.MyClass ). Behind the scenes this is just used to resolve to the fully-qualified class names which are then used in the bytecode as well.

What is the use of converting source code to Java bytecode?, Java byte code is quite similar to P-code. It’s basically instructions for a fairly simple machine. That machine is intended to be an

Difference between JIT and JVM in Java

Java Virtual Machine (JVM) is used in the java runtime environment(JRE). The original JVM was conceived as a bytecode interpreter. This may come as a bit of a surprise because of performance problems. Many modern languages are meant to be compiled into CPU-specific, executable code. The fact that the JVM executes a Java program , however, helps address the major issues associated with web-based applications.

The fact that the JVM executes a Java program also helps to make it stable. Since the JVM is in charge, program execution is controlled by it. Therefore, it is possible for the JVM to build a limited execution area called a sandbox that contains the software, preventing the system from getting unlimited access. Protection is also improved by some limitations in the Java language that exists. Java’s JVM architecture includes a class loader, execution engine , memory field, etc.

In order to understand differences, let’s dig down to the components by illustrating the working of JVM alongside.

• ClassLoader: The class loader has the purpose of loading class files. It helps accomplish three main functions: Loading, Initialization, and Linking.
• JVM language Stacks: Java memory stores local variables, and partial results of a computation. Each thread has its own JVM stack, created as the thread is created. When the method is invoked, a new frame is created, and then removed.
• Method Area: JVM Method Area specializes in storing the metadata and code-behind files for Java applications.
• PC Registers: The Java Virtual Machine Instruction address currently being executed is saved by PC registers. Each thread in Java has its own separate PC register.
• Heap: In a heap are saved all objects, arrays, and instance variables . This memory is shared between several threads.
• Execution Engine: It is a form of software used for the testing of software, hardware, or complete systems. The test execution engine never carries any information concerning the product being tested.
• Native Method Libraries which are the Executing Engine needs Native Libraries (C, C++) and the native method interface which is a framework for programming is the Native Method Interface. This enables the Java code that runs in a JVM to call libraries and native applications . Also, the native method stacks have a native code command depending on the native library. It assigns storage to native heaps or uses any stack type.

Just In Time(JIT) compiler

While Java was developed as an interpreted language , in order to improve performance , there is nothing about Java that prevents bytecode compilation into native code on the fly. For that reason, not long after Java’s initial release, the HotSpot JVM was released. A just-in- time (JIT ) bytecode compiler is included in HotSpot. A Just In Time(JIT) compiler is part of the JVM and on a piece-by-piece demand basis, selected portions of bytecode are compiled into executable code in real-time. That is, as is necessary during execution, a JIT compiler compiles code. In addition, not all bytecode sequences are compiled, only those that will benefit from the compilation. The just-in-time method, however, still yields a major boost in inefficiency. The portability and safety function still exists even though dynamic compilation is applied to bytecode since the JVM is still in control of the execution environment.

In order to understand differences, let’s dig down to the components by illustrating the working of JIT alongside.

Interpreting the bytecode, the standard implementation of the JVM slows the execution of the programs. JIT compilers interact with JVM at runtime to improve performance and compile appropriate bytecode sequences into native machine code .

Hardware is interpreting the code instead of JVM (Java Virtual Machine). This can lead to performance gains in the speed of execution. This can be done per-file, per-function, or maybe on any arbitrary code fragment; the code is often compiled when it’s close to being executed (hence the name “just-in-time”), and then cached and reused later without having to be recompiled. It performs many optimizations: data analysis, translation from stack operations to registry operations, reduction of memory access by registry allocation, elimination of common sub-expressions.

Hence, from the above knowledge, we landed on the conclusive differences between them as mentioned in the table below:

What is the purpose of bytecode in Java?, Bytecode allows any language to be compiled to bytecode — not just Java. There are plenty of other languages that can compile to bytecode.

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