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Oops In Java Pdf Download
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Shelli Frisby
Jan 1, 2024, 4:14:22 PM1/1/24
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Abstraction is the concept of hiding the internal details and describing things in simple terms. For example, a method that adds two integers. The internal processing of the method is hidden from the outer world. There are many ways to achieve abstraction in object-oriented programmings, such as encapsulation and inheritance. A Java program is also a great example of abstraction. Here java takes care of converting simple statements to machine language and hides the inner implementation details from the outer world.
oops in java pdf download
Download https://enpo-qdiko.blogspot.com/?xws=2x0KMy
Encapsulation is the technique used to implement abstraction in object-oriented programming. Encapsulation is used for access restriction to class members and methods. Access modifier keywords are used for encapsulation in object oriented programming. For example, encapsulation in java is achieved using private, protected and public keywords.
Inheritance is the object-oriented programming concept where an object is based on another object. Inheritance is the mechanism of code reuse. The object that is getting inherited is called the superclass and the object that inherits the superclass is called a subclass. We use extends keyword in java to implement inheritance. Below is a simple example of inheritance in java.
So I understand the compressed oops is enabled by default in HotSpot VM now. It has support for this from Java SE 6u23 onwards through the VM option -XX:+UseCompressedOops. I understand that it allows for efficient CPU cache utilization as the CPU caches can hold a larger number of references than if they had to deal with 64 bit sized references. But what I do not understand is how using only 32 bits JVM can address up to 264 addresses.
Compressed oops represent managed pointers (in many but not all places in the JVM software) as 32-bit object offsets from the 64-bit Java heap base address. Because they're object offsets rather than byte offsets, they can be used to address up to four billion objects (not bytes), or a heap size of up to about 32 gigabytes. To use them, they must be scaled by a factor of 8 and added to the Java heap base address to find the object to which they refer.
On an LP64 system, a machine word, and hence an oop, requires 64 bits, while on an ILP32 system, oops are only 32 bits. But on an ILP32 system there is a maximum heap size of somewhat less than 4Gb, which is not enough for many applications. On an LP64 system, though, the heap for any given run may have to be around 1.5 times as large as for the corresponding ILP32 system (assuming the run fits both modes). This is due to the expanded size of managed pointers. Memory is pretty cheap, but these days bandwidth and cache is in short supply, so significantly increasing the size of the heap just to get over the 4Gb limit is painful.
Compressed oops represent managed pointers (in many but not all places in the JVM) as 32-bit values which must be scaled by a factor of 8 and added to a 64-bit base address to find the object they refer to. This allows applications to address up to four billion objects (not bytes), or a heap size of up to about 32Gb. At the same time, data structure compactness is competitive with ILP32 mode.
In the interpreter, oops are never compressed. These include JVM locals and stack elements, outgoing call arguments, and return values. The interpreter eagerly decodes oops loaded from the heap, and encodes them before storing them to the heap.
In compiled code, oops are compressed or not according to the outcome of various optimizations. Optimized code may succeed in moving a compressed oop from one location in the managed heap to another without ever decoding it. Likewise, if the chip (i.e., x86) supports addressing modes which can be used for the decode operation, compressed oops might not be decoded even if they are used to address object fields or array elements.
In the C++ code of the HotSpot JVM, the distinction between compressed and native oops is reflected in the C++ static type system. In general, oops are often uncompressed. In particular C++ member functions operate as usual on receivers (this) represented by native machine words. A few functions in the JVM are overloaded to handle either compressed or native oops.
A 32-bit zero value decodes into a 64-bit native null value. This requires an awkward special path in the decoding logic, to the point where it is profitable to statically note which compressed oops (like klass fields) are guaranteed never to be null, and use a simpler version of the full decode or encode operation.
We can sometimes use a similar trick with compressed oops, by unmapping the first page or so of the virtual addresses used by the managed heap. The idea is that, if a compressed null is ever decoded (by shifting and adding to the heap base), it can be used for a load or store operation, and the code still enjoys an implicit null check.
Compressed oops use an arbitrary address for the narrow oop base which is calculated as java heap base minus one (protected) page size for implicit NULL checks to work. This means a generic field reference is next:
Theoretically it allows to save the heap base add (current Register Allocator does not allow to save register). Also with zero base the null check of compressed oop is not needed.
Current code for decoding compressed oops looks like this:
Zero based implementation tries to allocated java heap using different strategies based on the heap size and a platform it runs on.
First, it tries to allocate java heap below 4Gb to use compressed oops without decoding if heap size
If it fails or heap size > 4Gb it will try to allocate the heap below 32Gb to use zero based compressed oops.
If this also fails it will switch to regular compressed oops with narrow oop base.
Is there any plan to increase the range of compressed oops beyond 32 GBytes? Although 32 GBytes obviously fits nicely with the x86 addressing modes and requires only 8 byte object alignment it imposes a significant limitation on the use of an important technical advance. We are seeing pretty stonking benefits from compressed oops in benchmarks of our real-world cache applications. Although there are some obvious disadvantages of increasing the range (e.g. intruction pipeline effects on intel and the need for 16 or 32 byte object alignment in heap) our tests of building openjdk with 64 GByte compressed oop support and running our largest java applications indicates that there continue to be significant performance and heap size benefits with 64 GBytes of compressed oops.
I was just browsing through the source code around markOop and noticed the 64bit cms size stuff, so that lead me to look at freeChunk.hpp in the CMS stuff with it's special mark word (for 64bit compressed oops), followed by two machine word linked list pointers.
I was just wondering if you guys gave any thought to making these _prev, _next pointers compresses oops in this case, or is it clear that there are so few object types that can fit their fields in the spare 32 bits of a compressed oop header that the space savings would be irrelevant (i.e. making the minimum size of a CMS tenured generation object 2 words not 3)?
Hello, folks a Java newbie here. I am looking forward to ace OOPs concepts in Java. What are some resources you would recommend be it on youtube, udemy or blogs to get started with java? Any help would be highly appreciated.
What is the benefit of using encapsulation in java programming?
Well, at some point of time, if you want to change the implementation details of the class EmployeeCount, you can freely do so without affecting the classes that are using it.
JavaJavaJava is one of the majorly used general-purpose programming language designed to have no or limited implementation dependencies. Java requires a software platform for its compiled programs to be executed. Oracle and Android SDK are a few examples of the software platforms on which Java executes its programs. is a fast, secure, and reliable programming language, first released in 1995 by Sun Microsystems. Ever since it has expanded in its reach and functionality. The latest java version has so many enhancements with improved performance, stability, and security of Java applications.
OOPS, or Object-Oriented Programming system, is a fundamental concept in programming. If you are from a technical background, an interviewer expects you to know about OOPs. To make sure you do not miss the chance in your following interview, we have assembled basic and advanced oops interview questions.
In this article we are going to introduce you to one of the JVM optimizations known as Compressed oops. The idea of compressed oops is raised from the differences between 32bit and 64bit architecture. So we will have a very short review of 64bit architecture and then go deeper into the topic of compressed oops. At the end we will see it all in action with a simple example.
The example code for this article is rather simple, so we are not going to use any IDE. Compressed oops makes no sense on a 32bit machine. Also it is not activated by default in JDKs prior to 6u23. So we assume you are using a 64bit JDK newer than 6u23. The final tool we need is a memory analyzer tool. For this example we used industry standard Eclipse Memory Analyzer Tool version 1.5.
The ExampleProgram class from the simple program in the first lesson of Part 1 is a programmer-written class that uses the java.lang.System class from the Java platform API libraries to print a character string to the command line.
Classes in the Java platform API libraries define a set of objects that share a common structure and behavior. The java.lang.System class used in the example defines such things as standard input, output, and error streams, and access to system properties. In contrast, the java.lang.String class defines character strings.
One object-oriented concept that helps objects work together is inheritance. Inheritance defines relationships among classes in an object-oriented language. In the Java programming language, all classes descend from java.lang.Object and implement its methods.
35fe9a5643
oops in java pdf download
Download https://enpo-qdiko.blogspot.com/?xws=2x0KMy
Encapsulation is the technique used to implement abstraction in object-oriented programming. Encapsulation is used for access restriction to class members and methods. Access modifier keywords are used for encapsulation in object oriented programming. For example, encapsulation in java is achieved using private, protected and public keywords.
Inheritance is the object-oriented programming concept where an object is based on another object. Inheritance is the mechanism of code reuse. The object that is getting inherited is called the superclass and the object that inherits the superclass is called a subclass. We use extends keyword in java to implement inheritance. Below is a simple example of inheritance in java.
So I understand the compressed oops is enabled by default in HotSpot VM now. It has support for this from Java SE 6u23 onwards through the VM option -XX:+UseCompressedOops. I understand that it allows for efficient CPU cache utilization as the CPU caches can hold a larger number of references than if they had to deal with 64 bit sized references. But what I do not understand is how using only 32 bits JVM can address up to 264 addresses.
Compressed oops represent managed pointers (in many but not all places in the JVM software) as 32-bit object offsets from the 64-bit Java heap base address. Because they're object offsets rather than byte offsets, they can be used to address up to four billion objects (not bytes), or a heap size of up to about 32 gigabytes. To use them, they must be scaled by a factor of 8 and added to the Java heap base address to find the object to which they refer.
On an LP64 system, a machine word, and hence an oop, requires 64 bits, while on an ILP32 system, oops are only 32 bits. But on an ILP32 system there is a maximum heap size of somewhat less than 4Gb, which is not enough for many applications. On an LP64 system, though, the heap for any given run may have to be around 1.5 times as large as for the corresponding ILP32 system (assuming the run fits both modes). This is due to the expanded size of managed pointers. Memory is pretty cheap, but these days bandwidth and cache is in short supply, so significantly increasing the size of the heap just to get over the 4Gb limit is painful.
Compressed oops represent managed pointers (in many but not all places in the JVM) as 32-bit values which must be scaled by a factor of 8 and added to a 64-bit base address to find the object they refer to. This allows applications to address up to four billion objects (not bytes), or a heap size of up to about 32Gb. At the same time, data structure compactness is competitive with ILP32 mode.
In the interpreter, oops are never compressed. These include JVM locals and stack elements, outgoing call arguments, and return values. The interpreter eagerly decodes oops loaded from the heap, and encodes them before storing them to the heap.
In compiled code, oops are compressed or not according to the outcome of various optimizations. Optimized code may succeed in moving a compressed oop from one location in the managed heap to another without ever decoding it. Likewise, if the chip (i.e., x86) supports addressing modes which can be used for the decode operation, compressed oops might not be decoded even if they are used to address object fields or array elements.
In the C++ code of the HotSpot JVM, the distinction between compressed and native oops is reflected in the C++ static type system. In general, oops are often uncompressed. In particular C++ member functions operate as usual on receivers (this) represented by native machine words. A few functions in the JVM are overloaded to handle either compressed or native oops.
A 32-bit zero value decodes into a 64-bit native null value. This requires an awkward special path in the decoding logic, to the point where it is profitable to statically note which compressed oops (like klass fields) are guaranteed never to be null, and use a simpler version of the full decode or encode operation.
We can sometimes use a similar trick with compressed oops, by unmapping the first page or so of the virtual addresses used by the managed heap. The idea is that, if a compressed null is ever decoded (by shifting and adding to the heap base), it can be used for a load or store operation, and the code still enjoys an implicit null check.
Compressed oops use an arbitrary address for the narrow oop base which is calculated as java heap base minus one (protected) page size for implicit NULL checks to work. This means a generic field reference is next:
Theoretically it allows to save the heap base add (current Register Allocator does not allow to save register). Also with zero base the null check of compressed oop is not needed.
Current code for decoding compressed oops looks like this:
Zero based implementation tries to allocated java heap using different strategies based on the heap size and a platform it runs on.
First, it tries to allocate java heap below 4Gb to use compressed oops without decoding if heap size
If it fails or heap size > 4Gb it will try to allocate the heap below 32Gb to use zero based compressed oops.
If this also fails it will switch to regular compressed oops with narrow oop base.
Is there any plan to increase the range of compressed oops beyond 32 GBytes? Although 32 GBytes obviously fits nicely with the x86 addressing modes and requires only 8 byte object alignment it imposes a significant limitation on the use of an important technical advance. We are seeing pretty stonking benefits from compressed oops in benchmarks of our real-world cache applications. Although there are some obvious disadvantages of increasing the range (e.g. intruction pipeline effects on intel and the need for 16 or 32 byte object alignment in heap) our tests of building openjdk with 64 GByte compressed oop support and running our largest java applications indicates that there continue to be significant performance and heap size benefits with 64 GBytes of compressed oops.
I was just browsing through the source code around markOop and noticed the 64bit cms size stuff, so that lead me to look at freeChunk.hpp in the CMS stuff with it's special mark word (for 64bit compressed oops), followed by two machine word linked list pointers.
I was just wondering if you guys gave any thought to making these _prev, _next pointers compresses oops in this case, or is it clear that there are so few object types that can fit their fields in the spare 32 bits of a compressed oop header that the space savings would be irrelevant (i.e. making the minimum size of a CMS tenured generation object 2 words not 3)?
Hello, folks a Java newbie here. I am looking forward to ace OOPs concepts in Java. What are some resources you would recommend be it on youtube, udemy or blogs to get started with java? Any help would be highly appreciated.
What is the benefit of using encapsulation in java programming?
Well, at some point of time, if you want to change the implementation details of the class EmployeeCount, you can freely do so without affecting the classes that are using it.
JavaJavaJava is one of the majorly used general-purpose programming language designed to have no or limited implementation dependencies. Java requires a software platform for its compiled programs to be executed. Oracle and Android SDK are a few examples of the software platforms on which Java executes its programs. is a fast, secure, and reliable programming language, first released in 1995 by Sun Microsystems. Ever since it has expanded in its reach and functionality. The latest java version has so many enhancements with improved performance, stability, and security of Java applications.
OOPS, or Object-Oriented Programming system, is a fundamental concept in programming. If you are from a technical background, an interviewer expects you to know about OOPs. To make sure you do not miss the chance in your following interview, we have assembled basic and advanced oops interview questions.
In this article we are going to introduce you to one of the JVM optimizations known as Compressed oops. The idea of compressed oops is raised from the differences between 32bit and 64bit architecture. So we will have a very short review of 64bit architecture and then go deeper into the topic of compressed oops. At the end we will see it all in action with a simple example.
The example code for this article is rather simple, so we are not going to use any IDE. Compressed oops makes no sense on a 32bit machine. Also it is not activated by default in JDKs prior to 6u23. So we assume you are using a 64bit JDK newer than 6u23. The final tool we need is a memory analyzer tool. For this example we used industry standard Eclipse Memory Analyzer Tool version 1.5.
The ExampleProgram class from the simple program in the first lesson of Part 1 is a programmer-written class that uses the java.lang.System class from the Java platform API libraries to print a character string to the command line.
Classes in the Java platform API libraries define a set of objects that share a common structure and behavior. The java.lang.System class used in the example defines such things as standard input, output, and error streams, and access to system properties. In contrast, the java.lang.String class defines character strings.
One object-oriented concept that helps objects work together is inheritance. Inheritance defines relationships among classes in an object-oriented language. In the Java programming language, all classes descend from java.lang.Object and implement its methods.
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