public void extender(){
GraphicsEnvironment env =
GraphicsEnvironment.getLocalGraphicsEnvironment();
this.setMaximizedBounds(env.getMaximumWindowBounds());
this.setExtendedState(this.getExtendedState() | this.MAXIMIZED_BOTH);
}
// Deberás importar
//import java.awt.GraphicsEnvironment;
y llamas al metodo justo despues del initComponents();
sample
public NewJFrame() {
this.setUndecorated(true);
initComponents();
extender();
}
int xx;
int yy;
private void formMousePressed(java.awt.event.MouseEvent evt) {
xx=evt.getX();
yy=evt.getY();
}
private void formMouseDragged(java.awt.event.MouseEvent evt) {
int x =evt.getXOnScreen();
int y=evt.getYOnScreen();
this.setLocation(x-xx, y-yy);
}