Java access to Ethereum contract

1.

The smart contract has been written for a long time

if they can add changes, the description is centralized

the contract is written into the Ethereum smart contract, which is a contradiction sentence

the financial customer service doesn't understand, which is very unreliable

community sites

2. Gas & gt; ethestimateGas({ from:ethaccounts [1], to: ethaccounts[2], value:50000000000000 }) 21001 > Ethgasprice 2000000000, as shown above, shows this account [1] = & gt; The transaction of account [2] needs 21001 gas, and the current gasprice is 2000000000. How many gas does it take to send transaction / call contract method in Ethereum

3. Ethereum is a distributed computing platform. It generates an cryptocurrency called ether. Programmers can write "smart contracts" on the Ethereum blockchain, and these Ethereum smart contracts will be executed automatically according to the code

what is Ethereum
Ethereum is often compared with bitcoin, but the situation is different. Bitcoin is a kind of cryptocurrency and distributed payment network, which allows bitcoin to be transferred between users

related: what is bitcoin? How does it work

Ethereum has a bigger goal. As Ethereum says, "Ethereum is a distributed platform running smart contracts.". These smart contracts run on "Ethereum virtual machine", a distributed computing network composed of all devices running Ethernet nodes

"distributed platform" means that anyone can set up and run an Ethereum node just as anyone can run a bitcoin node. Anyone who wants to run "smart contracts" on nodes must pay the operators of these nodes in ether, which is a cryptocurrency related to Ethereum. Therefore, the person running the Ethernet node provides computing power and gets paid in the Ethernet, which is similar to the way that the person running the bitcoin node provides hash power and pays in bitcoin

in other words, although bitcoin is only a blockchain and payment network, Ethereum is a distributed computing network, and its blockchain can be used for many other things. Details are provided in the Ethereum white paper

what is ether
Ethernet is a digital token (or cryptocurrency) related to Ethereum blockchain. In other words, Ethereum is the token and Ethereum is the platform. But now people often use these terms alternately. For example, coinbase allows you to buy Ethereum, which stands for Ethereum

this is technically "altcoin", which actually means a non bitcoin cryptocurrency. Like bitcoin, ether is supported by distributed blockchain - in this case, Ethereum blockchain

developers who want to create applications or Ethereum smart contracts on Ethereum blockchain need Ethernet token to pay for nodes to host it, while users of Ethereum based applications may need Ethernet to pay for services in these applications. People can also sell services outside the Ethereum network and accept Ethernet payments, or they can sell Ethernet tokens in cash - just like bitcoin

5. As long as you can pay the deposit, choose the right direction.

6. There is no inevitable relationship between whether the virtual currency will disappear or not and whether it can not be used on the third-party platform. Online third-party trading platform can only say that this kind of currency has another platform for trading, which shows that this kind of currency is more reliable
Ruitai coin has not been launched on the third-party platform, but it is rumored that it will also be launched on the third-party platform.

7.

Generally speaking, the steps of deploying smart contract are as follows:

1. start an Ethereum node (such as geth or testrpc)

2. use Solc to compile smart contracts=& gt; Get the binary code

3. deploy the compiled contract to the network This step will consume Ethernet currency, and you need to use the default address or specified address of your node to sign the contract.)=& gt; Get the blockchain address and ABI of the contract (JSON representation of the contract interface, including variables, events and callable methods) The author confused ABI with contract interface here. ABI is the binary representation of the contract interface.)

4. use the JavaScript API provided by web3.js to call the contract Depending on the type of call, it may consume Ethernet currency.)

8. I've just seen Percy Jackson and the robber of divine fire. It's a bit like Harry Potter, but I think it's very good-looking. It's a story with Greek mythology
Percy Jackson is an ordinary 12-year-old boy who was diagnosed with dyslexia and hyperactivity disorder. During a field trip organized by the school, he was interviewed by his algebra teacher; Specific function & quot; Scared me. After that, Percy Jackson found that he was not an ordinary person, but a mythical figure and a descendant of human beings< After discovering the mystery of his life, Percy Jackson was sent to a special school. The children studying in this school are the offspring of many mythical characters. When Percy Jackson came to school, Poseidon immediately declared Jackson his own child. In this school, Percy Jackson met two good friends. One is the beautiful Annabeth chase, the descendant of Athena, the goddess of wisdom and skill; The other is Grover Underwood, a descendant of orcs. Not long in the school, Percy Jackson was accused by the gods of stealing the thunder rod of Zeus. Percy Jackson is required to hand over his thunder wand within 10 days, otherwise, his mother will be killed by these gods, and the war between the gods is inevitable...

there is still one minute left: three discriminated high school students have invented a time machine that allows them to go back in time and change their social status, And help other unfairly treated children to avoid the humiliation of discrimination in high school
twilight 2, new moon and 1 are about vampires. Bella (Kristen Stewart) is 18 years old and her father gives her a gift. Edward (Robert Pattinson) shows her love generously and tells her the legend of the Italian vampire king. Edward's red haired sister Alice (Ashley Greene, Ashley Greene) holds a birthday party specially for Bella. During the party, Bella accidentally cuts her arm and is attacked by Gaspar. Only with Edward's protection can she escape. However, since then, Edward graally alienated Bella and proposed to break up. This makes Bella cold, but Edward also has difficulties, still secretly protect Bella. Bella is in the empty window period, and her old friend Jacob (Taylor Lautner) makes a warm call, which makes their relationship warm up. Since then, Bella because of the cliff rescue, just know that Jacob is a werewolf, specialized in dealing with vampires. At the same time, Edward, who didn't know about it, thought Bella had committed suicide and was disheartened. He came to Italy to ask the royal family to end his life...

bloodthirsty daybreak, I think the ending is a little ironic
2012 is also very good, and the fantasy show of Arthur and his mini kingdom is also very good

9. In solidness, a contract consists of a set of code (contract function) and data (contract state). The contract is located at a special address on the Ethereum blockchain. uint storedData; This line of code declares a state variable, named storeddata, of type uint (256 bits unsigned integer). You can think of it as a storage unit in a database. Just like managing a database, you can query and modify it by calling functions. In Ethereum, usually only the owner of the contract can do so. In this example, the functions set and get are used to modify and query the values of variables, respectively

like many other languages, when accessing state variables, it is not necessary to add a prefix such as this

this contract can't do a lot (limited by Ethereum's infrastructure), it just allows anyone to store a number. And anyone in the world can access this number. There is no reliable way to protect the number you publish. Anyone can call the set method to set a different number to cover your published number. But your numbers will remain in the history of blockchain. Later we'll learn how to add an access limit so that only you can change the number

token example

the next contract will implement a cryptocurrency in the simplest form. Taking money in the air is no longer a magic trick. Of course, only the person who creates the contract can do it (it's also very easy to use other currency issuance modes, just to realize the differences in details). And anyone can send money to others, without registering a user name and password, as long as there is a pair of Ethereum public and private keys

note
this is not a good example for online solidness environments. If you use the online solidity environment to try this example. The address of from cannot be changed when the function is called. So you can only play the role of a coiner, you can cast money and send it to others, but you can't play the role of others. This online solidity environment will be improved in the future.