State design pattern is a behavioral design pattern that is use for

defining the state machine for an object. Each state of an object is

defined in a child class of State class. When different actions are

taken on an Object, it can change its state.

Strategy pattern is also a behavioral pattern, but it is mainly used

for defining multiple algorithms. With same action of a client, the

algorithm to be used can change.

Some people consider State pattern similar to Strategy pattern,

since an Object changes its Strategy with different method

invocations. But the main difference is that in State pattern internal

state of an Object is one of the determining factors for selecting the

Strategy for change of state.

Where as in Strategy pattern, client can pass some external

parameter in input during method invocation that determines the

strategy to be used at run time.

Therefore State pattern is based on the Object’s internal state,

where as Strategy pattern is based on Client’s invocation.

State pattern is very useful in increasing the maintainability of the

code in a large code-base.

https://medium.com/javarevisited/micro-biology-of-state-and-strategy-design-pattern-2add63460ab7