He has been playing the piano for ten years. He wants to be a pianist.

[Alice Chu]

Please tell me if my understanding is correct.

1. He has been playing the piano for two hours. He will take a break in ten minutes.
It means the single action of playing the piano started two hours ago and has continued up to the present, and he is still playing the piano now.

2. He has played the piano for three hours. Now he is resting and having some tea.
It means the single action of playing the piano lasted for three hours and was finished before now. It is linked to the present.

3. He has played the piano for ten years. He wants to be a pianist.
It means the repeated action of playing the piano lasted for ten years until now. He still plays the piano now. We emphasize the time period, ten years.

4. He has been playing the piano for ten years. He wants to be a pianist.
It means the repeated action of playing the piano lasted for ten years until now. He still plays the piano now. We emphasize the ongoing action, playing the piano.

 

[5jj]

1. He has been playing the piano for two hours. He will take a break in ten minutes.
It means the single action of playing the piano started two hours ago and has continued up to the present, and he is still playing the piano now.

It could mean that. We could also say that sentence about someone who has stopped for a cigarette break every thirty minutes.

2. He has played the piano for three hours. Now he is resting and having some tea.
It means the single action of playing the piano lasted for three hours and was finished before now. It is linked to the present.

Fine. We could also say that sentence about someone who has stopped for a cigarette break every thirty minutes. We could also use the progressive form in that sentence.

 

[Rover_KE]

3. He has played the piano for ten years. He wants to be a pianist.

He is already a pianist. Perhaps you mean 'He wants to be a professional/cruise ship/concert pianist.