Material UI error: Invalid hook call. Hooks can only be called inside of the body of a function component

I tried to convert the Example Functional component ( https://github.com/mui-org/material-ui/blob/master/docs/src/pages/getting-started/page-layout-examples/sign-in/SignIn.js ) to Class component. After changing I am getting the following error

Invalid hook call. Hooks can only be called inside of the body of a function component. This could happen for one of the following reasons:
1. You might have mismatching versions of React and the renderer (such as React DOM)
2. You might be breaking the Rules of Hooks
3. You might have more than one copy of React in the same app
See https://fb.me/react-invalid-hook-call for tips about how to debug and fix this problem.

This is my current code

import React from 'react';
import Avatar from '@material-ui/core/Avatar';
import Button from '@material-ui/core/Button';
import CssBaseline from '@material-ui/core/CssBaseline';
import TextField from '@material-ui/core/TextField';
import FormControlLabel from '@material-ui/core/FormControlLabel';
import Checkbox from '@material-ui/core/Checkbox';
import Link from '@material-ui/core/Link';
import Grid from '@material-ui/core/Grid';
import Box from '@material-ui/core/Box';
import LockOutlinedIcon from '@material-ui/icons/LockOutlined';
import Typography from '@material-ui/core/Typography';
import { makeStyles } from '@material-ui/core/styles';
import Container from '@material-ui/core/Container';

const useStyles = makeStyles(theme => ({
    '@global': {
        body: {
            backgroundColor: theme.palette.common.white,
        },
    },
    paper: {
        marginTop: theme.spacing(8),
        display: 'flex',
        flexDirection: 'column',
        alignItems: 'center',
    },
    avatar: {
        margin: theme.spacing(1),
        backgroundColor: theme.palette.secondary.main,
    },
    form: {
        width: '100%', // Fix IE 11 issue.
        marginTop: theme.spacing(1),
    },
    submit: {
        margin: theme.spacing(3, 0, 2),
    },
}));

class SignIn extends React.Component {

    state = {
        userName: '',
        password: '',
    }

    render() {
        const classes = useStyles();
        return (
            <Container component="main" maxWidth="xs">
                <CssBaseline />
                <div className={classes.paper}>
                    <Avatar className={classes.avatar}>
                        <LockOutlinedIcon />
                    </Avatar>
                    <Typography component="h1" variant="h5">
                        Sign in
                    </Typography>
                    <form className={classes.form} noValidate>
                        <TextField
                            variant="outlined"
                            margin="normal"
                            required
                            fullWidth
                            id="email"
                            label="Email Address"
                            name="email"
                            autoComplete="email"
                            autoFocus
                        />
                        <TextField
                            variant="outlined"
                            margin="normal"
                            required
                            fullWidth
                            name="password"
                            label="Password"
                            type="password"
                            id="password"
                            autoComplete="current-password"
                        />
                        <FormControlLabel
                            control={<Checkbox value="remember" color="primary" />}
                            label="Remember me"
                        />
                        <Button
                            type="submit"
                            fullWidth
                            variant="contained"
                            color="primary"
                            className={classes.submit}
                        >
                            Sign In
                         </Button>
                        <Grid container>

                        </Grid>
                    </form>
                </div>
            </Container>
        );
    }
}

export default SignIn;