Invalid new expression of abstract class type

#include "myhighlighter.h"
#include <QTextCharFormat>
#include <QDebug>

myhighlighter::myhighlighter(QWidget *parent) : QSyntaxHighlighter(parent)
{
    QDebug("myhighlighter initiated");
}

void myhighlighter::highlightblock(const QString &text)
{
    QTextCharFormat format;
    QRegExp rx(pattern);
    if(!rx.isValid() || rx.isEmpty() || rx.exactMatch("")){
        setFormat(0,text.length(),format);
    }
    format.setBackground(Qt::yellow);
    int index = rx.indexIn(text);
    while(index >= 0)
    {
        int length = rx.matchedLength();
        setFormat(index,length,format);
        index = rx.indexIn(text , length + index);
    }
}

#ifndef MYHIGHLIGHTER_H
#define MYHIGHLIGHTER_H
#include <QSyntaxHighlighter>
#include <QTextDocument>
#include <QString>

class myhighlighter : public QSyntaxHighlighter
{
    Q_OBJECT
public:
    explicit myhighlighter(QWidget *parent = 0);
virtual void highlightblock(const QString &text)=0;
    void setPattern(QString str){ pattern = str ; }
private:
    QString pattern;
};

#endif // MYHIGHLIGHTER_H

#include <QFile>
#include <QKeyEvent>
#include "myhighlighter.h"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    QFont font;
    font.setFamily("monokai");
    font.setStyleHint(QFont::Monospace);
    font.setFixedPitch(true);
    font.setPointSize(10);
    ui->textEdit->setFont(font);
    ui->textEdit->acceptRichText();
    const int tabStop = 4;  // 4 characters
    QFontMetrics metrics(font);
    ui->textEdit->setTabStopWidth(tabStop * metrics.width(' '));
    this->setCentralWidget(ui->textEdit);
    highlighter = new myhighlighter(this);     // here i get the error
    highlighter->setDocument(ui->textEdit->document());
    // highlighter->setPattern(QString("class"));
    // highlighter->highlightblock(QString(""));
}