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TB stands for the Invoices TimeBills module. TE stands for the Expenses module. TA stands for the Timesheets module. Probably Difference Between abstract Class and Interface is the most frequent question being asked in the. Net world.   In this tutorial, I will explain the differences theoretically followed by code snippets. Theoretically there are basically 5 differences between Abstract Classes and Interfaces as listed below. A class can implement any number of interfaces but a subclass can at most use only one abstract class. An abstract class can have non abstract methods concrete methods whereas all methods of interfaces must be abstract. An abstract class can declare or use any variables whereas an interface is not allowed to do so. The following code compiles properly since no field declaration is in the interface. Test. Interfaceint x 4   Filed Declaration in Interfacevoid get. Method string get. Name abstract class Test. Abstract. Classint i 4 int k 3 public abstract void get. Class. Name It will generate a compile time error as Error. Interfaces cannot contain fields. So we need to omit the Field Declaration to compile the code properly. Test. Interfacevoid get. Method string get. Name  abstract class Test. Abstract. Classint i 4 int k 3 public abstract void get. Class. Name An abstract class can have a constructor declaration whereas an interface cannot. So the following code will not compile interface Test. Interface Constructor Declarationpublic Test. Interfacevoid get. Method string get. Name abstract class Test. Abstract. Classpublic Test. Abstract. Classint i 4 int k 3 public abstract void get. Class. Name The code above will generate the compile time error Error 1 Interfaces cannot contain constructors  So we need to omit the constructor declaration from the interface to compile our code. The following code compiles perfectly interface Test. Interfacevoid get. Method string get. Name abstract class Test. Abstract. Classpublic Test. Abstract. Classint i 4 int k 3 public abstract void get. Class. Name An abstract class is allowed to have all access modifiers for all of its member declarations whereas in an interface we cannot declare any access modifier including public since all the members of an interface are implicitly public. Note here I am talking about the access specifiers of the member of interfaces and not about the interface. The following code will explain it better. It is perfectly legal to provide an access specifier as Public remember only public is allowed. Test. Interfacevoid get. Method string get. Name The code above compiles perfectly. It is not allowed to provide any access specifier to the members of the interface. Test. Interfacepublic void get. Method public string get. Name The code above will generate the compile time error Error 1 The modifier public is not valid for this item. But the best way of declaring an interface will be to avoid access specifiers on interfaces as well as members of interfaces. Testvoid get. Method string get. Name 2. What is the difference between overriding and overloadingOverloading. In this approach we can define multiple methods with the same name changing their signature. In other words different parameters. This can be performed within a class as well as within a child class. Doesnt require any permission from the parent for overloading its method in the child. Overriding. It is an approach of defining multiple methods with the same name and the same signature. This can be performed only under child classes. Requires an explicit permission from the parent to override its methods in the child. String Builder and String class String A string is a sequential collection of Unicode characters that represent text. String is a class that belongs to the namespace System. String.  String concatenation can be done using the opearator or the String. Concat method. The String. Concat method concatenates one or more instances of a String. Sample code string string. Today is   Date. Time. Now. To. String D  . Console. Write. Line string. Hi   This is Jitendra string. Sampathi. Rao. Console. Write. Linestring. String. Builder. String. Builder is a class that belongs to the namespace System. Text. This class cannot be inherited. In String. Builder we use the Append  method. Sample code. String. Builder number new String. Builder 1. 00. 00 for int i 0 ilt 1. Number. Append i. To. String So where do we use these classesThe answer is for simple String manipulations we can use the String class. But when there are more string manipulations it is better to use the String. Builder class.  Why is the String. Builder class better for more string manipulations instead of the String class The String object is immutable. Every time you use one of the methods in the System. String class, you create a new string object in memory, that requires a new allocation of space for that new object. In situations where you need to perform repeated modifications to a string, the overhead associated with creating a new String object can be costly. The performance of the application might be degraded. So we use String. Builder in such cases. A String. Builder object is mutable. The System. Text. String. Builder class can be used when you want to modify a string without creating a new object. For example, using the String. Builder class can boost performance when concatenating many strings together in a loop. Differences between String and String. Builder. It belongs to String namespace. It belongs to String. Text namespace. String object is immutable. Delhi Metro Full Route Map. String. Builder object is mutable. Assigning String. Builder sbuild new String. Buildersomething important Assigning String s something important We can use the operator or Concat method to concatenate the strings. We use the Append method. When string concatenation is done, additional memory will be allocated. Here additional memory will only be allocated when the string buffer capacity is exceeded. What is the difference  between array and array list Mirosoft. Net has many namespaces for many purposes. Among them the System. Collections is a very important namespace in the programmers perceptive. While coding, we look for classes that can reduce manual operation. For instance if you want to sort the values in an array then you need to do the manual operations. Here obviously we look for the classes that can automate the sorting by just calling a method. In other words we can call this namespace as a utility namespace. Let us see the classes in this namespace. Collection Classes. The System. Collections namespace has many classes for the individual purpose. We will discuss the frequently used classes in this article. Array. List. Bit. Array. Stack. Queue. Comparer. Hash. Table. Sorted. List. Array. List. The Array. List is one of the important classes in the System. Collection namespace. We can say it is the next generation of the Array in C. Array. List is a dynamic array it will increase the size of the storage location as required. It stores the value as an object. The allocation of the Array. List can be done through the Trim. To. Size property. Methods. 1Add. It will add the element as object in the Array. List. 2Add. Range. It will add the collections of elements in the object as individual objects in the Array. List. 3Clear. It will clear the all objects in the Array. List. 4Binary. Search. Developer Guide Bitcoin. Find detailed information about the Bitcoin protocol and related specifications. BETA This documentation has not been extensively reviewed by Bitcoin experts and so likely contains numerous errors. Please use the Issue and Edit links on the bottom left menu to help us improve. Click here to close this disclaimer. XThe Developer Guide aims to provide the information you need to understand. Bitcoin and start building Bitcoin based applications, but it is not a. To make the best use of. Bitcoin. Core, either from source or from a pre compiled executable. Questions about Bitcoin development are best asked in one of the. Bitcoin development communities. Errors or suggestions related to. Bitcoin. org can be submitted as an issue. In the following documentation, some strings have been shortened or wrapped. If you hover your mouse over a paragraph, cross reference. If you hover over a cross reference link, a brief. Block Chain. The block chain provides Bitcoins public ledger, an ordered and timestamped record. This system is used to protect against double spending. Each full node in the Bitcoin network independently stores a block chain. When several nodes all. The validation rules these. This section describes many of. Bitcoin Core. Block Chain Overview. The illustration above shows a simplified version of a block chain. A block of one or more new transactions. Copies of each transaction are hashed, and the hashes are then paired. The merkle root is stored in the block header. Each block also. stores the hash of the previous blocksheader, chaining the blocks. This ensures a transaction cannot be modified without. Transactions are also chained together. Bitcoin wallet software gives. Each. transaction spends the satoshis previously received in one or more earlier. A single transaction can create multiple outputs, as would be. Any subsequent reference is a forbidden double. Outputs are tied to transaction identifiers TXIDs, which are the hashes. Because each output of a particular transaction can only be spent once. Unspent Transaction Outputs UTXOs or spent transaction outputs. For a. payment to be valid, it must only use UTXOs as inputs. Ignoring coinbase transactions described later, if the value of a. Bitcoin. miner who creates the block containing that. For example, in the illustration above, each transaction spends 1. Proof Of Work. The block chain is collaboratively maintained by anonymous peers on the network, so. Bitcoin requires that each block prove a significant amount of work was invested in. Chaining blocks together makes it impossible to modify transactions included. As a. result, the cost to modify a particular block increases with every new block. The proof of work used in Bitcoin. A good cryptographic hash algorithm converts arbitrary data into a. If the data is modified in any way and. To prove you did some extra work to create a block, you must create a. For. example, if the maximum possible hash value is 2. In the example given above, you will produce a successful hash on average every other try. You can even estimate the probability. Bitcoin assumes a linear probability that the lower it makes the target threshold, the more hash attempts on average will need to be tried. New blocks will only be added to the block chain if their hash is at. Every 2,0. 16 blocks, the network uses timestamps stored in each. The ideal value is. If it took fewer than two weeks to generate the 2,0. If it took more than two weeks to generate the blocks, the expected. Note an off by one error in the Bitcoin Core implementation causes the. Because each block header must hash to a value below the target. Bitcoin network expended. Only if you acquired a majority of the networks hashing power. The block header provides several easy to modify fields, such as a. Also, only the 8. IO, and adding additional. Block Height And Forking. Any Bitcoin miner who successfully hashes a block header to a value. These blocks are commonly addressed. Bitcoin. block block 0, most commonly known as the genesis block. For example. block 2. Multiple blocks can all have the same block height, as is common when. This. creates an apparent fork in the block chain, as shown in the. When miners produce simultaneous blocks at the end of the block chain, each. In the absence of. Eventually a miner produces another block which attaches to only one of. This makes that side of. Assuming a fork only contains valid. Stale blocks are also sometimes called orphans or orphan blocks, but. Long term forks are possible if different miners work at cross purposes. Since multiple blocks can have the same height during a block chainfork, block. Instead, blocks. are usually referenced by the hash of their header often with the byte order reversed, and in hexadecimal. Transaction Data. Every block must include one or more transactions. The first one of these. The UTXO of a coinbase transaction has the special condition that. This temporarily. Blocks are not required to include any non coinbase transactions, but. All transactions, including the coinbase transaction, are encoded into. The rawtransaction format is hashed to create the transaction. From these txids, the merkle tree is constructed by pairing each. If there are. an odd number of txids, the txid without a partner is hashed with a. The resulting hashes themselves are each paired with one other hash and. Any hash without a partner is hashed with itself. The. process repeats until only one hash remains, the merkle root. For example, if transactions were merely joined not hashed, a. ABCDEEEE Merkle root. ABCD EEEE. . AB CD EE E is paired with itself. A B C D E. Transactions. As discussed in the Simplified Payment Verification SPV subsection. The full peer does not need to be trusted it is. For example, to verify transaction D was added to the. SPV client only needs a copy of the C, AB, and EEEE hashes in addition to the. If the five transactions in this block were all at. Note If identical txids are found within the same block, there is a possibility that the merkle tree may collide with a block with some or all duplicates removed due to how unbalanced merkle trees are implemented duplicating the lone hash. Since it is impractical to have separate transactions with identical txids, this does not impose a burden on honest software, but must be checked if the invalid status of a block is to be cached. CVE 2. 01. 2 2. Consensus Rule Changes. To maintain consensus, all full nodes validate blocks using the same. However, sometimes the consensus rules are changed to. When the new rules are. A block following the new consensus rules is accepted by upgraded. For example, a new. A block violating the new consensus rules is rejected by upgraded. For example, an abusive. In the first case, rejection by non upgraded nodes, mining software. This creates permanently divergent chainsone for non upgraded. In the second case, rejection by upgraded nodes, its possible to keep. Thats because, in this case, non upgraded. This is called a soft. Although a fork is an actual divergence in block chains, changes to the. For example, increasing the block size above 1 MB. In this example, an actual block chainfork is. Consensus rule changes may be activated in various ways. During Bitcoins. Satoshi Nakamoto performed several soft forks by just. Multiple soft forks such as BIP3. Such forks activated via a flag day are known as. User Activated Soft Forks UASF as.