Android - Resize UI widget created dynamically

I try to create a button dynamically with in Java and add it some constraints to position it in the center of my constrainLayout. So I write this code:

import android.app.Activity;
import android.os.Bundle;
import android.support.constraint.ConstraintLayout;
import android.support.constraint.ConstraintSet;
import android.widget.Button;
public class SelectGameActivity extends Activity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_select_game); ConstraintSet constraintSet = new ConstraintSet(); ConstraintLayout constraintLayout = findViewById(R.id.constraintLayout); constraintSet.clone(constraintLayout); Button button = new Button(this); button.setText("test"); button.setId(213); constraintLayout.addView(button); constraintSet.connect(button.getId(), ConstraintSet.LEFT, R.id.constraintLayout, ConstraintSet.LEFT); constraintSet.connect(button.getId(), ConstraintSet.RIGHT, R.id.constraintLayout, ConstraintSet.RIGHT); constraintSet.connect(button.getId(), ConstraintSet.TOP, R.id.constraintLayout, ConstraintSet.TOP); constraintSet.connect(button.getId(), ConstraintSet.BOTTOM, R.id.constraintLayout, ConstraintSet.BOTTOM); constraintSet.applyTo(constraintLayout); }
}

It works but the button fills all the screen:

I think it is because my button doesn't have any specific height and width. I tried several codes to give it a size but no effect. Could someone give me some hints to resize my button correctly ?

Thank you very much !

Charles