入力フィールドからテキストを取得..

public class MainActivity extends AppCompatActivity {

    Button btn;
    TextView textView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        btn = findViewById(R.id.btn);
        textView = findViewById(R.id.editText);

        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String input = textView.getText().toString().trim();
                TextView text = findViewById(R.id.result);
                text.setText(input);
                Log.d("View", input);
            }
        });
    }

}