An interface in Solidity defines functions without implementation. Another contract can inherit the interface and must implement all of its functions. An interface differs from an abstract contract because all functions in an interface have no implementation, while an abstract contract can have some implemented functions. Interfaces are useful for standardizing function signatures across contracts.

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S O L I D I T Y
I N T E R F A C E

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What it is ?
What is interface in
solidity ?

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Interface
Where all the functions does not have implementation (function body)
pragma solidity ^0.4.0;
interface member{
function setName() public returns (string);
function setAge() public returns (uint);
}

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Abstract Contract Vs Interface
Contract become abstract when at
least one of the function in that
contract does not have
implementation.
In interface all the functions does not
have implementation
Abstract Contract Interface

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Use of Interface
Another contract can inherit interface and need to implement all of the functions.
pragma solidity ^0.4.0;
interface member{
function setName() public returns (string);
function setAge() public returns(uint);
}
contract teacher is member{
function setName() public returns(string){
return "Mark";
}
function setAge() public returns(uint){
return 32;
}
}